This is a list of Freeware games. But not just any freeware. These are, at the time of writing, the cream of the crop.
ABA Games is this Japanese guy that makes ultra-stylish and very unique shooters. Every game he makes has something to make it special, and they are all tons of fun. In particular I recommend Gunroar, but again, they're all great.
Windows: http://www.asahi-net.or.jp/~cs8k-cyu/index_e.html
Linux: http://www.emhsoft.com/
It's Doom as a 2D platform game. Controls mimic a first person shooter, you can shoot 360 degrees. Don't play in a dark room at night.
Windows: http://www.webpages.uidaho.edu/~scot4875/
Linux/OS X: http://www.labyrinth.net.au/~trandor/abuse/
An action/platformer with puzzle elements where you pilot a hot air balloon through the fires of hell and shoot ghosts with an umbrella. Can be frustrating at times, but it's usually really fun. Has a ton of levels.
Windows: http://www.rjbsoftware.co.uk/afterlife_download.php
A great turn-based strategy game. Plays kind of like Advance Wars once you get into it. I haven't actually played too far in, but it looks very professional.
Windows/Linux/OS X: http://www.wesnoth.org/
A humorous adventure game following the adventures of a hapless Aurthor Dent-type character who finds himself trapped in a bleak future.
Anything: http://www.scummvm.org/downloads.php
Top-down retro-style multiplayer game. A lot of popular modes from first person shooters in a game that looks vaguely like asteroids. Great LAN party game.
Windows/Linux?/OS X: http://bitfighter.org
This game is a must-play. An action platformer in the tradition of Metroid, but a little bit heavier in terms of plot. You play as a robot who wakes up in an underground world without any memory left. The controls are great, the learning curve is awesome, and the story is worth checking out also. Could easily have been a professional game in the 16-bit era. Download and see for yourself. A revamped version will be on WiiWare soon, but the PC version has remained free.
Windows: http://agtp.romhack.net/doukutsu.html
OS X: http://www.nakiwo.com/software.htm
This was one of the big games that popularized the real-time strategy genre. EA has released the ISOs for free. Windows only, but the game actually runs significantly better under Wine in Linux than it does on Windows XP.
Disk 1: http://www.gamershell.com/download_20863.shtml
Disk 2: http://www.gamershell.com/download_20864.shtml
EA has released "Command and Conquer: Red Alert" for free to promote the release of Red Alert 3.
Windows: http://www.ea.com/redalert/news-detail.jsp?id=62
A game that would probably be more suited for the Nintendo DS. A shooter in which you draw lines with the mouse to defeat your foes.
Windows: http://www.konjak.org/chalk.htm
A Chinese made shmup, there's nothing too special about it except that it's really well made and plays great (and the graphics are nothing to sniff at either). Definitely download if you're a fan of this type of game.
Windows: http://www2.tky.3web.ne.jp/~yosshin/my_works/index.html
A goofy action rpg that's a lot of fun in addition to being quite funny. You play a lowly pig farmer who, in the tradition of this type of game, is thrust into an epic quest. The key to the game is its great sense of humor. There are also a lot of fan-made scenarios for download as well.
Windows: http://www.rtsoft.com/dink/
A bizarre little roguelike/civilization colony management game. Guide dwarves through the construction of a gigantic mountain dwelling, defenses of aforementioned dwelling, elephants, creatures from beyond, and more until their eventual demise! Quite a steep learning curve. Runs under Wine quite well.
Windows: http://www.bay12games.com/dwarves/index.html
Turnbased "puzzle game in the tradition of Adventures of Lolo or Chip's Challenge." Do you feel like feeling stupid today? This is a very, very difficult puzzle game. The intro is easy enough, but things get very hard very fast when you start playing levels other gamers have designed.
Windows/OS X/Linux: http://escape.spacebar.org/
Another action platformer, this one has a J-RPG style storyline. I haven't played far enough yet to say too much about it, but the link below has a good review.
Windows: http://www.acid-play.com/download/eternal-daughter/
A multi-player only version of the popular horror FPS, F.E.A.R.
Windows: http://www.joinfear.com
Odd little timewaster in which your microorganism eats other microorganisms in order to grow. The first segment is fairly short. Worth a playthrough at least once, if just to see what happens at the end. PS3 version in the works.
Windows/OS X/Linux: http://intihuatani.usc.edu/cloud/flowing/
A mature clone of Civilization II. What more do you need to know?
Windows/Linux/OS X: http://www.freeciv.org/index.php/Freeciv
Though actually a commercial game, the license agreement allows non-commercial distribution between friends and acquaintances. If you know someone who owns the game, get them to make you a copy. ;-)
Windows/Linux/OS X
A really creative game that blends Asteroids with an RTS. Again I haven't played too much, but the tutorial was a lot of fun. Should be great to play online. It is an earlier work by the author of the PS3/Steam game Everyday Shooter.
This would make a really nice laptop game since it dosen't rely on a mouse or a whole lot of processing power.
Windows/Linux: http://www.queasygames.com/gate88/downloads.html
Steal cars, commit bank robberies, and run over people. Rockstar has officially released this rather controversial game for free, along with it's predecessor. Not for children. There are better games for adults also, come to think of it.
Windows: http://www.rockstargames.com/classics/
A spiritual successor to the X-Box Live Arcade game Geometry Wars. It's wonderful fun and highly addictive, so give it a download.
Windows: http://www.incitti.com/Blitz/ (Scroll down for the download link)
Older Linux/OS X versions: http://gridwars.marune.de/
An excellent remake of an old isometric puzzle game. You guide two dog-like creatures through puzzle filled mazes. The catch is that you can switch between them and send them off in different directions to use their unique strengths ala the Lost Vikings. Definitely worth a try.
Windows/Linux/OS X/BeOS: http://retrospec.sgn.net/games/hoh/downloads.html
Flashback-ish platform game which caters to wildly different play-styles. Upgrades can be used to increase your destructive powers or allow you to survive longer while playing peacefully. How the story unfolds depends on how you play.
Windows: http://www.remar.se/daniel/iji.php
A blast from 1993, this game sets you in 100 deadly one-screen levels. Armed with only a jetpack, a welding torch, and your amazing tactics, your objective is to grab all the gems in the level. While being pursued by killer robots, of course. Sort of a futuristic version of lode runner. Includes a level editor. Formally shareware, now released by the author as freeware.
DOS: http://www.adeptsoftware.com/jetpack/
Part exploration, part challenge, part ZZT. Knytt Stories is a beautiful little platformer with nice pixel-art, and a level editor. Nine worlds were available at launch, and many more have been created since then.
Windows: http://nifflas.ni2.se/index.php?main=02Knytt_Stories
A simple monocromeish action dungeon crawler. Roam around a randomly generated dungeon with a simple shockwave weapon. Surprisingly entertaining.
Windows: http://www.asceai.net/meritous/
Very nice little side scrolling shooter. R-Type-like-ish. Feels almost like a commercial Game Boy Advance title. Lots of unlockable ships and levels. The unlockable ping pong game is frustratingly addicting.
Windows: http://www.vector.co.jp/soft/win95/game/se444925.html
A platform game with an advanced physics engine. Guide a ninja through trap filled mazes. One of the most frustrating games ever created. You will love to hate it. The sequel, N+, is on Xbox, PSP, and Nintendo DS, but this game has remained free.
Windows/ Linux /OS X: http://www.harveycartel.org/metanet/downloads.html
Really fun ninja minigame. Pass through levels as quickly and quietly as possible without alerting guards. Includes grappling hook with... alternative uses.
Windows: http://users.tkk.fi/~jjsalon2/
This is the definitive non-scrolling time-trial ninja-rope 2D platform game. No other entry even comes close in this exclusive field. Complete with uzi-propulsion, matrix-vision, and a hyphen-filled description.
Windows/Linux: -http://www.evildrbin.com/ninjah/-
(The domain has expired. Temporary mirror of the Windows version at http://files.filefront.com/Ninjahzip/;11265493;/fileinfo.html )
This is, without doubt, the oldest, hardest, most in-depth game on this list. If you own an device known as a "computer", chances are that NetHack will run on it. It's a dungeon-crawl type role playing game, ala Dungeons and Dragons. The goal is to guide your ASCII character through a ASCII dungeon, retrieve the Aumlet of Yendor and return to the surface. What's neat is that you can pretty much do anything, though it might not look like it at first glance. There's a reason it's been maintained and played for over 20something years. Go check it out.
http://www.olywa.net/cook/nhack.htm - Optional tileset for graphic mode. Much better then the default one, imho.
Pick a character from one of four races and help them survive being stranded on an alien world. You have to keep your character warm and fed (and not eaten), all while scavenging parts and exploring your surroundings in order to find escape. Great graphics and great control. Great everything.
Windows: http://www.monkkonen.net/notrium.php
The best fighting game ever to come to PC. Not that there was a whole lot of competition or anything. Instead of the usual blood-and-guts fare, this one involves giant robots.
DOS: http://www.dosgamesarchive.com/download/game/66
A great point-and-click adventure game inspired by old Lucasarts adventures. A funny story with great characters, and pretty much everything you could ask for in a game of this type. Definitely a must-play.
http://outoforder.adventuredevelopers.com/
A cross between Pokemon and a horizontal shooter. Build up your collection of ships and fly them in order to level them up. Extremely addicting.
Windows: http://www.pixelships.com/pxs_details.html
Free multiplayer FPS. Apparently quite good.
Windows: http://www.planetwolfenstein.com/files/files.shtml
Imagine a real time strategy game where each unit is a human player. That's Savage in a nutshell. One player, the "commander" manages his base and team from an overhead RTS view, and everyone else plays as a soldier on the field in a third-person hack-n-slash or FPS view. Players level up as they fight, and gain new units and abilities as the commander traverses the tech-tree. Very heavily team-based, very dependent on good commanders, and a lot of fun. Formally commercial, now freeware to promote Savage 2.
Windows / Linux: http://www.s2games.com/savage/
A exploration/collection platformer. The game doesn't need an explanation because it doesn't give one. Just trust me when I say it's really cool.
Windows: http://autofish.net/clysm/art/video_games/seiklus/
A 3rd-person 3D networked mech battle game. If you like multiplayer deathmatch games and anime mechs equiped with jetpacks duking it out in the middle of a city with fighter jets swooping in and out firing homing missiles, this might be the game for you.
Windows: http://www.acid-play.com/download/silver-knights/
An insane sideview actioner designed for online play. Think Halo meets Liero. Plenty of game modes such as deathmatch and capture the flag, and plenty of ways to kill each other = plenty of fun.
Windows: http://www.acid-play.com/download/soldat/
A great space privateering. What that basically means is it's Sid Meir's Pirates in space. I actually think it's better than Pirates. In any case it's very very very good. Download.
Windows/Linux/OS X: http://sc2.sourceforge.net
Hey, kids! What sort of FPS games with vehicular combat did people play before Halo came out? Answer: Stuff like this.
Windows: http://www.gamershell.com/download_6159.shtml
Thank you, alphabetical order. You always save the best for last. This game is a shmup where you fight an endless stream of bosses. They start out small, but get bigger and bigger and change depending how you defeat them. Perhaps the most addicting thing ever created. It's so simple, but so playable, and so fun. Get it.
Windows: http://www18.big.or.jp/~hikoza/Prod/index_e.html
Aw, forget alphabetical order. Fraxy fits better here. It's very much like Warring Forever, but with user created bosses.
Windows: http://mokeron.hp.infoseek.co.jp/zg/fraxy_main.html
Celshaded multiplayer FPS with a heavy focus on doing wall jumps based on the Quake 2 engine, you say? We have you covered. Worth a look, if only for the celshading.
Windows/Linux: http://www.warsow.net/
Yes, this is indeed, as the name might imply, a near pixel perfect port of the NES Legend of Zelda game. Not only that, but it includes a map editor for custom quests. If you've ever wanted to beat Legend of Zelda, but hated how ugly the graphics were, there is also an included graphically enhanced remake of the original. Very nice.
Windows: http://www.zeldaclassic.com/
Betas releases, include Linux & OS X: http://www.allegro.cc/depot/ZeldaClassic/
A truly ancient game engine with integrated editor. Everything is displayed in ASCII characters. Try the default worlds for a bit, then go download some fan creations. Truly, some amazing stuff has been generated by fans. There is no "official" ZZT site, so the link points to Cly5m's ZZT page. Really, quite a good jumping off point.
DOS: http://www.autofish.net/creation/video_games/zzt/
The ultimate file compression tool. It can handle just about any thing you throw at it. ZIP, RAR and LZH are just three of the formats it can compress and extract.
Windows/Linux: http://www.7-zip.org
Handy for those old apps that Windows XP won't support correctly. It's a nice emulator mainly used for running DOS games.
Windows/Linux: http://dosbox.sourceforge.net
1up's Weekly Freeplay - http://www.google.com/search?hl=en&q=site%3A1up.com+weekly+freeplay&btnG=Google+Search
Independant Gaming Blog - http://indygamer.blogspot.com/
Best Freeware Games of 2007 - http://www.gamespot.com/pages/forums/show_msgs.php?topic_id=25943291
101 Free Games 2007- http://www.1up.com/do/feature?cId=3156339
101 Free Games 2008 - http://www.1up.com/do/feature?cId=3165201
Freeware game of the day - http://forums.tigsource.com/index.php?topic=703.0
GameTap (Free commercial games rotated in and out) - http://www.gametap.com/video-games/free-games
Links and ideas from a lot of places and people have been mashed together to make this site.
This is my site. I maintain this list.
http://www.penny-arcade.com/forums/viewtopic.php?t=1073827066
This is where the base list origenated. I have taken it upon myself to expand upon and more widely distribute the content.
http://autofish.net/index.html
This is where the idea first came to me, and where I first discovered a lot of the games on this site.