Regarding games, there aren't a huge amount, but some great ones are Xonotic,
MegaGlest, OpenArena, SuperTuxKart, Warzone 2100, Torus Trooper, Tremulous,
Minetest, Red Eclipse, and Ryzom.
Some great non-3D games are many of the games by Kenta Cho (my favorites are
Torus Trooper and Tumiki Fighters), Teeworlds, X-Moto, Secret Maryo
Chronicles, Ri-li, Pingus, NetHack, LBreakout2, LTris, Liquid War, Scavenger,
OpenClonk, Rocks'n'Diamonds, FreeCiv, and Endgame: Singularity.
There are many, many more, but these are ones that I've personally played and
that are high-quality, though most have graphics that are "outdated" (the
most modern of these in terms of graphics and sound are Xonotic, Red Eclipse,
and OpenClonk, I think).
