No-Action Jackson
http://www.talesofinterest.com/no-action/
Genre: Adventure
Ryan jokingly said, "Hey, this is my life story!" after seeing No-Action Jackson in motion. NAJ is a full-on tribute to the original LucasArts adventures of years past, focusing on the life of a D&D/PC gaming freak (translation: us). Anyhow, the dialogue is funny and the graphic style is fantastically reminiscent of Day of the Tentacle. The price is most definitely right (free, that is), but I would've been ready to pay for this game.
Half-Life 2: The Hidden -- Source
http://mods.moddb.com/5133/downloads/Hidden-Source/
Genre: Shooter
They should just call this thing Half-Life Predator. A squad of players gears up and hunts through maps to find the invisible stalker (another player). He who scores the most points becomes the Hidden in the next round. Sounds easy? It isn't. It's vicious watching Shawn play, spraying bullets into thin air only to find that he is really the prey. Intense and paranoid fun, this is what F.E.A.R. should have done with multiplayer mode.
Steam Brigade
http://www.pedestrianentertainment.com/steambrigade/
Genre: Real-time Strategy
Now, I may be alone on this one, but raise your hands if you remember the classic Apple II game Rescue Raiders. It was kind of like Choplifter (operating a helicopter in an action game on a 2D, left-to-right scrolling map) but it added the strategy element of grabbing bunkers, deploying units, and ultimately taking over the enemy base. I was retarded for this game, played it all the damn time. Now, a steampunk-centric tribute is out there and worth playing. Steam Brigade looks fantastic and sends me back. Call up troops and march 'em across enemy lines. Start playing this game at your own risk.
Grid Wars
http://www.incitti.com/Blitz/
Genre: Shooter
Hey, Xbox 360 owners: You all paid $5 to buy Geometry Wars, right? Well, hate to break it to you, but Grid Wars is just as good (if not better, I'll humbly submit), but you can download it right now with no strings attached. Save that five bucks for a bottle of beer or something.
(borrowed from the net.... I have no personal knowledge of any of these games)