I don't see Allegiance anywhere in that list. It's a space combat/RTS game.
Also not mentioned are Tribes 1 and 2. They were made freeware to commemorate the disappointing Tribes: Vengeance, but I'm not sure where to link them. Oh well, here's a PlanetTribes link, a Tribes 1 3DGamers link, and a Tribes 2 FilePlanet link. (I don't know about this "no Tribes 2 keys left" crap, since I bought a boxed copy a few months before it went freeware and just use that.)
Finally, I prefer http://www.gameflaws.com/cavestory as a Cave Story link. I'm not saying the AGTP one's bad or anything, but you can find more CS-related stuff here. Plus, there's a link to the AGTP page somewhere in there.
Those issues aside, this is quite a convenient thread.
EDIT: Changed the Tribes 1 link to 3DGamers.com, since FilePlanet apparently wanted money from you just to D/L the game. Couldn't find a Tribes 2 D/L link on 3DGamers. Haven't checked anywhere else.