Created by Justin Fisher in 1994, this was the first total conversion ever made and one of the most famous. It took six months to finish. Originally for Doom, it has since been updated for the sequel and Ultimate Doom. The mod became so popular several game developers actually offered Fisher a job although he turned them down to finish college.

David Lobser, Mike Dickson, and Dan Goldwasser released this Doom mod on December 11th, 1994. It includes 6 new monsters: the Xenomorph, the Ceiling Xenomorph, the Baby Xenomorph, the Face Hugger, the Loader (run by Weyland-Yutani employees who don't want you to ruin their research), and the Alien Queen. Barrels have also been replaced with Eggs.

Chris Dennett and Kenneth Peng finished this TC on August 17th, 1995. Version 1.31 came out on November 22nd, 1995. Enemies include Facehuggers, Eggs (and Facehuggers will jump out of them if you don't destroy them quick enough), Spitting Aliens, Soldier Aliens, and the Queen. The M92F Pistol, the Pump-Action Shotgun, the M41A Pulse Rifle, the M56 Smart Gun, the M240 Flamethrower, and the Power Loader.

The game takes place on LB4-28 (meant to be LV-428), the site of one of the Colonial Marines' ammunition dumps. Xenomorphs were found in the base's sewage system. They overrun the troops at the compound. You were out on a routine patrol mission on the far side of the planet. Once you get outside the radio distortions of the nearby mountains, you try to make contact with the marines at the base, but no one answers. Assuming the worst, you head back.

Though still in beta, Michael Gummelt programmed this mod for Doom and Ultimate Doom (Doom 2 is not supported). All kinds of Aliens make an appearance in it including spitters, soldiers, facehuggers, eggs, egg layers, etc. Plus, it has helper marines (with voice samples from the second film) and enemy marines paid off by the company. You can choose to play as Ripley, Hudson, Hicks, Vasquez, or even the Doom Marine. Weapons include double pistols, the flamethrower, smart gun, grenade launcher, mine layer, double barrel shotgun, etc.

Mr. Pink authored this Doom TC. It has 27 new levels with updated sounds and graphics including the Pulse Rifle, Warrior Alien, etc.

Tyson Geller created this Ultimate Doom mod. It has single player, cooperative, and deathmatch all with new sounds and graphics.

This Doom 2 partial conversion has 3 single-player levels with new sounds, music, graphics, etc.

Available only as a demo, Cyberwaste Wads released this Doom 2 TC on October 10th, 2007.

Mark Fleig programmed this Wolfenstein 3D mod. With 8 original levels, the game's castle has been remade to look like the bowels of a space station, and the enemies have been replaced with Aliens.

In 1997, John Diamond, Dave Wallin, and Gustav Taxen created this TC. In addition to adding all the forms of the Alien (Egg, Facehugger, Chestburster, Warrior, Drone, Queen) as well as making new levels like the amazing Nostromo replica, they let players use all the weapons from Cameron's classic film: the H&K 9mm Pistol, Shotgun, M40 Pulse Rifle, M60 Autorifle, M56A Smart Gun, and Flamethrower along with the ability to switch to the Motion Tracker. 20th Century Fox threatened legal action against Alien Quake's authors, ordering them to cease all activities. Their website had to be taken down, and anyone offering the game for download was to be reported. Special thanks to Baron for the screenshots.

This Duke Nukem 3D TC has 28 levels and requires JDuke to run. Special thanks to the Duke Nukem 3D TC Site for the screenshots.

Released on July 22, 2004, this Duke Nukem 3D mod has 6 levels, ranging from a dark colony complex to a jungle. Special thanks to the Duke Nukem 3D TC Site for the screenshots.

Released on July 26, 1997, this Duke Nukem 3D mod has 4 levels. The shareware version of this TC doesn't include new enemies (they're just the original Duke Nukem ones), but that is supposed to be different for the full version (if you can find it). Once again, special thanks to the Duke Nukem 3D TC Site for the screenshots.

Bioko created this mod for Counter Strike: Source. Released in January of 2009, it lets the player battle all kinds of Aliens, not just the Xenomorph but also other monsters. The weapons haven't changed though (no Pulse Rifle). Neither has the music so it's still very much a Counter Strike game and not a true TC.

Tom Purcell was developing this 3-level deathmatch mod for Doom 2. Unfortunately, it wasn't finished, but the idea was to have each level represent a different film. The first was for Alien, the second for Aliens, and the third for Alien3.