What is it?

idTech1 is what powers the classic 1993 shooter Doom by id Software, as well as several other games. It was originally just called the Doom engine, due to it being first used for that game, but has since been retroactively called idTech 1 after id Software's later game RAGE was announced to be running on the idTech5 engine.

What's it matter?

Doom and its cousins are very fun games, and in the thirty years since Doom was released there has been an absolute treasure-trove of fan made content, with the community not only showing no signs of slowing down but there are more projects than ever being released on a regular basis.

This is made possible through the use of source ports, reimplementations of the source code into new executables that allow not only for playing the original games, but the vast array of fan-made content, much of which takes advantage of features not available in the original DOS version.

What do I do to play?

These days, the easiest way to play is to just purchase Doom + Doom II on Steam or GOG and play that. But sooner or later you're going to want to see what else is out there. At heart, all you really need is an IWAD (the main data file for Doom or one of its cousins) and a source port. (It is possible to play the original DOS exe via DOSBox, but that's only for die-hard nostalgia huffers. Chocolate Doom will give you the same experience with less hassle - more on that later.) However there are many, many, many mods and tools for you to get the most out of your Doom.

While different source ports may require different setups, the basic installation goes something like this:

Get the IWAD of your choice and put it into a folder
Get the source port of your choice and put it into the same folder
Run the .exe
Enjoy!

What am I looking for?

The following is a semi-comprehensive list of official, semi-official, and retail products using idTech 1, sorted in release order first by series, then main title, then expansions.

Doom (1993)

The scary, violent, sci-horror classic. This is the original, three-episode version of the game sold via mail order. This is now rare.

The Lost Episodes of Doom (1995)

A collection of maps by Chris Klie and Bob Carter, collected and sold as a commercial expansion pack for Doom alongside a strategy guide. Most of these maps are available online, rendering the pack essentially shovelware.

The Ultimate Doom (1995) Steam GOG

An updated version put in a box and sold in stores. This is the default version that is sold on game platforms like Steam.

SIGIL (2019) Steam GOG Romero.com

An unofficial expansion for Ultimate Doom designed by the legendary John Romero, one of the original game's designers. While nominally free, Romero's website sells a version with high-quality music by Buckethead.

SIGIL II (2023) Romero.com

A sequel to SIGIL, again designed entirely by John Romero. Again, while nominally free, Romero.com sells a version with high-quality music by Thorr.

Doom II: Hell on Earth (1994) Steam GOG

The official sequel to Doom, originally sold only in retail but now available in digital storefronts.

Master Levels for Doom II (1995) Steam GOG

An expansion pack for Doom II compiled by id Software based on contributions by hand-selected, talented mappers in the community, featuring 21 new levels, as well as a shovelware disc entitled Maximum Doom.

Hell to Pay (1996)

A partial conversion set two hundred years after the events of Doom II, where a new hero must rescue humanity from enslavement by the denizens of Planet Hell. Yeah.

Perdition's Gate (1996)

Developed by Team TNT member Tom Mustaine and his father, it was initially intended as a third level pack for Final Doom, but missed the window.

No Rest for the Living (2010) Steam GOG

An expansion pack originally made for the XBox Live Arcade release of Doom II; while unofficial, pirated versions floated around the internet for a while, there have been official PC releases in the years since.

Legacy of Rust (2024) Steam GOG

A brand-new, two-episode campaign for Doom II as part of the 2024 re-release, with new monsters and other features.

Mockup derived from Final Doom PSX.

Final Doom (1996) Steam GOG

A standalone sequel to Doom II, developed by Team TNT, that consists of two games, both independent of each other as well as Doom II. The first is TNT: Evilution, originally intended as a free Doom II mod before being picked up by id Software for a publication deal. The second is The Plutonia Experiment, this was designed entirely by a pair of brothers (who also helped work on Evilution) and commissioned directly by id Software.

Doom 64 (1997) Steam GOG

Originally exclusive to the Nintendo 64, this is not a port, but a very dark and scary sequel. Got an official remaster a few years ago.

Heretic (1994)

A dark fantasy-themed shooter very similar to Doom. This is the original, three-episode version of the game sold via mail order. This is now rare.

Heretic: Shadow of the Serpent Riders (1996) Steam GOG

An updated version put in a box and sold in stores. This is the default version that is sold on game platforms like Steam.

Hexen: Beyond Heretic (1995) Steam GOG

A thematic sequel to Heretic with a darker atmosphere and some RPG-like elements.

Hexen: Deathkings of the Dark Citadel (1996) Steam GOG

The only official expansion pack for Hexen. The only commercial expansion pack, period.

Strife: Quest for the Sigil (1996) Steam GOG
Veteran Edition (2014) Steam GOG

A quasi-RPG-like sci-fantasy game with heavy story focus and voice acting. Veteran Edition is a modern remaster with new features, but comes bundled with the original release as well.

Killing Time (PC version) (1996) Steam GOG
Resurrected (2014) Steam GOG

Believe it or not, the PC release of the cult classic 3DO shooter uses a heavily-modified version of the Jaguar Doom engine (which was coded by John Carmack himself and served as the basis for most of the subsequent console ports of Doom.)

Chex Quest (1996)

You read that right. Cooked up as a family-friendly, deliberately non-violent (for a given definition of non-violent) promotional stunt for Chex cereal and included in cereal boxes, it actually turned out to be pretty good. Had a couple of sequels.

HACX: Twitch 'n Kill (1997)

A commercially-sold add-on for Doom II that functions more like a total conversion, it's of solid historical value despite its somewhat unfinished state.

I can't believe it's not DOS!

The following is a list of commercial games made in the last several years utilizing the GZDoom engine. I'd initially considered leaving this out, but I figure despite being very far away from the original code by now, the GZDoom engine is still descended from id Software's early work.

The Forestale (2019) Steam

A true rarity, this is a 3D platformer in the GZDoom engine with a cartoony style.

Hedon: Bloodrite (2019) Steam

A dark fantasy steampunk shooter with a cool orc heroine. Two games, Hedon and Hedon II, combined into a single massive package!

Fury's Sky (2019) (Early Access) Steam

A 3D flight action game in the vein of Star Fox or Terminal Velocity.

SHRINE (2019) (free) Steam

A creepy body horror-themed shooter from scumhead, who has a penchant for this sort of thing.

SHRINE II (2020) (free) Steam

Liked SHRINE? Here's some more of it!

Dismantled (2020) Steam
Director's Cut (2022) Steam

An old-school-style survival horror shooter. If you like your horror to be a bit on the extreme end of things you can't go wrong with this -- the Director's Cut even got the Adults Only label!

Lycanthorn II: Rain of Beasts (2020) (free) Steam

Scumhead's sequel to the original Lycanthorn, a Castlevania-inspired short-form shooter. Comes packaged with the original game.

Vomitoreum (2021) Steam

Another scumhead game with an open world and a nightmarish, cosmic horror fantasy setting.

REKKR: Sunken Land (2021) Steam

A nordic fantasy shooter akin to Heretic. Lots of content.

Project Crypt (2022) (free) Steam

A 3D action-adventure game in the vein of classic Half-Life horror mods.

Hands of Necromancy (2022) Steam

Play a powerful necromancer who might be the only thing keeping your world from utter ruin in a neat gunpowder fantasy setting.

Hands of Necromancy II (2024) Steam

II Hands II Necro

Project Absentia (2022) (Early Access) Steam

A cartoony shooter inspired by old Flash animations and sprite comics of the early 2000s (if you remember any of this, make sure you schedule a colon cancer screening with your doctor.)

I am Sakuya: Touhou FPS Game (2022) Steam

Honestly I've seen weirder Touhou fan games.

Apocalyptic Vibes (2023) Steam

Another 3D shooter, inspired by the likes of S.T.A.L.K.E.R. and Metro. If you're done playing the Ashes series give this a try.

Supplice (2023) (Early Access) Steam

Heavily inspired by Doom and Marathon. Slated to have six episodes, three are out as of October 2024.

Sharpshooter 3D (2023) Steam

Russian Meme Simulator. Very rooted in Slavic culture, pretty in-your-face offensive, like a Russian Grezzo 2.

Twilight Town: A Cyberpunk FPS (2023) Steam

A strange, somewhat cartoony, very bloody cyberpunk shooter.

Twilight Manor: Roguelite FPS (2024) Steam

A roguelike followup to Twilight Town, set in the same universe.

A Fool's Art Gallery (2023) Steam

A virtual art gallery set in a liminal world.

Beyond Sunset (2023) (Early Access) Steam

A cyberpunk RPGFPS where you search the neon-soaked streets for lost memories.

Friendship Island (2024) Steam

A sci-fi/horror themed shooter with a comic book aesthetic.

Selaco (2024) (Early Access) Steam

A sci-fi/cyberpunk shooter heavily inspired by F.E.A.R. and other classic shooters of the late 90s/early 00s.

Relentless Frontier (2024) (Early Access) Steam

Explore a hostile alien planet in this sci-fi shooter.

Borrowhelen (2024) Steam

Gunpowder fantasy horror FPS with obvious strong inspiration from Blood.

Unhinged 2 (2025) Steam

Follow-up to the original Unhinged, a disturbing Silent Hill-inspired horror mod for Doom.

The Age of Hell (TBA) Steam

Action shooter heavily inspired by the Doom reboot, being developed by Doom community superstar BridgeBurner56.

Box Party (TBA) Steam

An abstract, MSPaint-esque cartoon shooter where you fight evil food.

Brutal Fate (TBA) Steam

Brutal Doom developer Marcos "Sergeant Mark IV" Abenante's commercial product. Expect just as much ludicrous violence!

DISDAIN (TBA) Steam

A Quake-inspired eldritch shooter using the VKDoom fork of GZDoom.

Enigmatic Worlds (TBA) Steam

An abstract shooter inspired by old Game Maker FPS games.

Hellslinger (TBA) Steam

Play some sort of furry demon gunslinger girl fighting your way out of Hell.

Mala Petaka (TBA) Steam

Kill aliens and portal-hop in this sci-fi shooter with a chunky pixel aesthetic.

Stellar Valkyrie (TBA) Steam

Try to rescue your girlfriend from a cult in this sci-fi shooter.

Popular source ports

Boom

The first major source port for Doom, developed by Team TNT (who were also behind Final Doom.) The first big source port was Boom, developed by Team TNT (the Final Doom developers.) In addition to removing limits and fixing bugs, it added a number of new mapping features. (See "standard" in the glossary.) Long discontinued, but its legacy and influence remains strongly felt. Supports all Doom games. Some popular projects using Boom: Phobos: Anomaly Reborn, Ancient Aliens.

Chocolate Doom

Intended to mimic the original DOS executable, without all the pesky DOSBox business. The name comes from the tradition of calling DOS-compatible mods "vanilla." (See the glossary below.) Supports all Doom games, Heretic, Hexen and Strife.

Crispy Doom

Like Chocolate, but with some QOL features like widescreen, removal of mapping limits, etc. deemed out-of-scope with Chocolate Doom. Supports all Doom games, Heretic, Hexen and Strife.

Doom + Doom II Steam GOG

A new official port running on the KEX framework, replacing the old Unity port. Seems to be a more robust experience with a very large collection of Doom games and addons including No Rest for the Living and the new Legacy of Rust.

Doom64EX+

An unofficial source port for the Doom 64 remaster. If the official port included with the remaster is not to your liking -- its performance is shit, tbh -- this is a good alternative that will automatically detect your install.

Doom Legacy

An absolute disaster of a source port that nevertheless was an early advanced engine, long-since overtaken by the likes of GZDoom. Very finicky on modern hardware, even with newer releases. Supports all Doom games and Heretic. Popular projects utilizing Doom Legacy: Twilight Warrior, Phobia: the Age (albeit with broken music.)

Doom Retro

Another Chocolate Doom fork, with features of its own like new visual effects, and support for all map standards up to MBF21. Supports all Doom games.

Doomsday

The one-time sovereign for fancy visual effects, but now strictly a niche source port with only partial Boom support and no support for later standards. Supports all Doom games, Heretic and Hexen. Popular(?) projects utilizing Doomsday: Doom 64: Absolution TC, Corridor 7: Alien Invasion TC.

DSDA-Doom

If you're looking for something closer to vanilla with some QOL features, DSDA-Doom is a popular option, spun off from PrBoom+. Optimized for speedrunning and demo recording. Compatible with Boom, MBF and MBF21 (more on these terms later.) Supports all Doom games, Heretic and Hexen. Projects utilizing DSDA-Doom: Fore/vr/ Alone.

EDGE-Classic

A continuation of the defunct EDGE source port, intended as an option for older or weaker machines. Supports all Doom games and Heretic. Popular projects utilizing EDGE/EDGE-Classic: QDoom, Immoral Conduct.

Eternity Engine

The less popular of two big modding-focused source ports. Originally intended for a now-defunct total conversion project. While not as popular as GZDoom, it still has many features of its own. Supports all Doom games and Heretic, Hexen and Strife support in progress. Popular projects utilizing Eternity: Mordeth, Heartland.

GZDoom

The big one. If you're looking for an authentic Doom experience this isn't it, too much has changed under the hood. But it is a solid choice for modding and fancy graphics, and is the engine of choice for commercial games like Selaco and Beyond Sunset. The most popular port. Supports all Doom games, Heretic, Hexen and Strife. Compatible with almost every map. Popular projects utilizing GZDoom: Ashes 2063, My House.

LZDoom

Like GZDoom but optimized for potatoes. May not fully support all GZDoom gameplay mods (likely just the ones that use a lot of fancy visual effects.) Otherwise supports everything GZDoom does.

MBF

An early successor to Boom by a former developer. Stands for "Marine's Best Friend." Introduces several new modding features, including the option for friendly monsters, including helper dogs. Likewise long-deprecated. While it was never popular (being bumped out of the market share by ZDoom) its modding features were too good for future source ports to pass up. Supports all Doom games. Popular projects utilizing its features: Valiant, Eviternity.

PrBoom+

A more recent successor to the Boom legacy. While discontinued, it's still a solid competitor to DSDA-Doom. Supports all Doom games. Popular projects utilizing PrBoom+: Comatose.

RZDoom

Picking up where ZDoom left off. Unlike GZDoom, maintains full backwards compatibility with the last version of ZDoom while playing nicer with modern machines. Supports everything ZDoom does.

Woof!

A modern continuation of the old MBF source port. Features many modern-day QOL features while remaining relatively faithful to MBF's original intentions. Ironically probably more popular as a source port than MBF ever was. Supports all Doom games.

ZDoom

The first really advanced source port, introducing a slew of new features. Long deprecated by GZDoom, but you might need it for something really old. (I would suggest using RZDoom instead.) Supports all Doom games, Heretic, Hexen and Strife. Popular projects using ZDoom: Action Doom 1 and 2, Knee Deep in ZDoom.

Where to get the games

Doom + Doom II 2024 Rerelease Steam GOG

Features Ultimate Doom, Doom II, Final Doom, Master Levels, No Rest for the Living, SIGIL, and the new campaign Legacy of Rust, as well as access to a number of other addons, all in one package.

Classic Doom bundle (best value) Steam

Comes with the above, plus Doom 64 and both the original Doom 3 and its expansion and the BFG Edition remaster.

The Lost Episodes of Doom

Out of print.

SIGIL II Romero.com

Hell to Pay Doomed Speed Demos Archive

Click the big blue hell2pay link at the top.

Perdition's Gate Doomed Speed Demos Archive

Click the big blue Perdition's Gate link at the top.

Heretic: Shadow of the Serpent Riders Steam GOG

Hexen: Beyond Heretic Steam GOG

Hexen: Deathkings of the Dark Citadel Steam GOG

Heretic/Hexen collection (best value) Steam GOG

Comes with Heretic: Shadow of the Serpent Riders, Hexen, Deathkings of the Dark Citadel, and Hexen II, but not Hexen II's expansion pack Portal of Praevus or Heretic II.

Strife: Quest for the Sigil Steam GOG
Strife: Veteran Edition Steam GOG

You get both the remaster (with its extended campaign and Capture the Chalice game mode) as well as the original DOS release to run in DOSBox or the source port of your choice.

Killing Time Steam GOG
Killing Time: Resurrected Steam GOG

The original 2015 re-release of the PC version with a bunch of fixes over the 1996 release, and the 2024 remaster with toggleable high-resolution graphics and extensive modding capabilities.

Chex Quest trilogy Charles Jacobi's website

A remaster of the original game that was included in boxes of Chex cereal, the sequel (really an add-on originally only available on the official Chex Quest website), and the official 2008 Chex Quest 3.

HACX Rich "Nostromo" Johnson's website

Features a fixed-up version 1.2 of the (basically unfinished) HACX. A version 2.0 has been in the works for years.

Where's all the WADs?

Looking for something to play? Check out the 100 Best Wads list, 1994-2003.

As well as twenty-plus years of Cacowards.

Keep up with new releases on the Doomworld forums.

And gameplay mods. (Hey my thread is pinned!)

And total conversions.

Check out projects on the ZDoom forums.

And there's always something new from the boys and girl(s?) at Doomer Boards.

How to play wads and mods

There are three ways to do this:

Drag a wad file over the .exe and hope for the best
Learn how your source port's command line works and make a batch file
Realize that those two options are a pain in the ass and get a launcher. ZDL is the popular one, I use Doom Launcher.

Reach out and touch someone

Wanna play multiplayer? You'll need two things: A multiplayer source port and a server browser.

Zandronum

The fancy port.

Odamex

The vanilla port.

Chocolate Doom

Also has native multiplayer support if you want it.

Doomseeker

The modern server browser.

Doom Explorer

Another popular choice, based on the old IDE launcher.

NukemNet

Features support for:

Doom (shareware, registered, Ultimate)
Doom II: Hell on Earth
Final Doom (Evilution, Plutonia)
Heretic (shareware, registered, Serpent Riders)
Hexen (demo, full, Deathkings)
Strife (demo, full)

Classic Gaming Arena

Features support for:

Doom (shareware, Ultimate)
Doom II: Hell on Earth
Final Doom (Evilution, Plutonia)
Heretic (shareware, Serpent Riders)
Hexen (demo, full, Deathkings)
Strife (demo, full)

Modding tools

If you're not planning to use a lot of mods, then this won't necessarily be of interest to you, but if you're interested in digging into the inner workings of mods you'll absolutely want to look at this list, even if you're just trying to figure out how to make mods work together.

WhackEd 4

The modern DEHACKED tool, useful for examining the .deh files to see what they alter.

Ultimate Doom Builder

The modern mapping tool. Fully-featured with a 3D mode. Nearly every new map these days -- from basic vanilla maps to crazy-complex commercial games -- is made in this.

SLADE 3

An all-in-one tool for examining and altering the contents of .wads, .pk3s and .pk7s. This is probably going to be your go-to tool for understanding how mods work. Some of the tools within this application have dedicated alternatives that might be better/easier to work with, but when you're just looking at stuff, this is what you want.

Glossary

ACS

A very simple scripting language, originally created for Hexen. ZDoom (GZDoom's predecessor) included support for ACS as part of implementing Hexen support, while also expanding on its capabilities; this expanded version is also available in Eternity Engine.

BEX

An extended version of DEHACKED for Boom-compatible source ports. Typically packaged in .bex files that can be loaded into source ports.

complevel

Short for compatibility level, referring to a preset that toggles various compatibility options in various source ports to allow certain wads to function properly. Typically defined by numbers, with 0-4 referring to various versions of Doom, 7-9 referring to various versions of Boom, and 21 referring to MBF21. See also: Standard.

DECORATE

A now-deprecated coding language for ZDoom-family source ports to introduce new monsters and other objects without altering existing code.

DEHACKED

The original means of modding Doom and still in use today given its broad compatibility. It originally functioned by means of directly altering DOOM.EXE; due to its nature, it could not be used to write new logic, only reuse existing routines, but that has not stopped modders from creating impressive partial and total conversions over the years. DEHACKED modifications can now be applied on-the-fly via .deh files. Some popular projects using extensive DEHACKED work: Batman Doom, D4V.

DEHEXTRA

An early attempt at expanding on the capabilities and limitations of DEHACKED. Not very popular. Projects utilizing DEHEXTRA: Black Ops, SMOOTHED.

DSDHACKED

A newer update of DEHACKED, removing nearly all its limits. Developed in tandem with the MBF21 specification, but not requiring it. Projects utilizing DSDHACKED: Smooth Doom MBF21.

ID24

A new standard, building on MBF21 and previous standards and introduced in the Doom + Doom II release. So far, only Legacy of Rust uses its features. See also: MBF21.

IPK3

Stands for "initial PK3." Used in GZDoom-based ports to tell the game this is the main data file, in .pk3 format. See also: IWAD, PK3.

IWAD

Stands for "initial WAD." Most of these are going to be the data files for commercial games, but it's possible to create new IWADs recognized by source ports. See also: PWAD, WAD.

limit-removing

The original DOS version was difficult to map for as there were hard limits on what the engine was capable of. Nearly all source ports remove these limits and fix bugs present in the original DOS version. Popular projects targeting this compatibility level: SIGIL I and II, Ultimate Doom in Name Only, most of the Doomer Boards Projects catalog.

MBF21

A new specification for future modding capabilities in source ports, developed in 2021 as an expansion of Boom and MBF features and several bugfixes. First implemented in the DSDA-Doom source port and now seeing support in other ports including GZDoom. Stands for "Modder's Best Friend." Popular projects utilizing its features: Eviternity II, Doom 2 in City Only.

PK3

Some source ports are capable of reading the contents of a zip or PK3 file, and some mods are packaged within these containers. PK3s are exactly the same as zip files. See also: WAD.

PK7

Some source ports are capable of reading 7zip format containers, usually given the PK7 extension.

PWAD

Stands for "Patch WAD." If it's not an IWAD, it's this, intended to "patch" over the IWAD to replace assets such as a new map or sound file. See also: IWAD, WAD.

Source port

An adaptation, usually done by fans utilizing freely-available code, of a game engine to function on different operating systems and hardware. Not to be confused (usually) with commercial ports such as the SNES version of Doom or the Nintendo 64 version of Quake.

Standard

An informal agreement among source port developers to include certain levels of support for editing features introduced by source ports. Known standards are: Boom, MBF, MBF21, ID24. While ZDoom and GZDoom maintain compatibility with prior standards (excluding ID24) their features are not generally seen outside of their own ecosystem.

Vanilla

Completely compatible with the original DOS version of the game. This includes DEHACKED usage. Popular projects targeting this compatibility level: The Darkening Episode 2, Suspended in Dusk.

WAD

Stands for "Where's All the Data?" This contains game assets -- both official and addon. Nearly every data file is going to use the .WAD extension regardless of whether it's the game itself or an addon.

ZScript

The modern GZDoom scripting language, partially supplanting DECORATE.

idTech 1