When I saw this post: https://www.adisc.org/forum/computer...ible-free.html about Marathon now being available for free, I thought of the other games that are now available for free from their developers, and did up a short list:
Elder Scrolls I: Arena
Elder Scrolls II: Daggerfall
Note: These two are fan-patched releases to run on modern systems. The unmodified version was available on The Elder Scrolls V: Skyrim , but the whole website was recently replaced by an ad for ES5:Skyrim
Grand Theft Auto, GTA2 and Wild Metal: all on this page. I can confirm GTA2 works on modern systems, haven't tried the other two.
Micropolis (aka Simcity 1): Installation is quite complicated, so instructions are in the link. Getting Micropolis
Also possibly playable online if you have a Maxis account. Registering a new one wouldn't work for me, others may have more luck.
Quake: Can't find the link, but id GPLed the source.
Quake III: As Quake Live
Alien Swarm: Requires Steam
Command and Conquer, Red Alert 1 and Tiberian Sun: Links on offical forums
Anyone else know of other major developers that released their games for free?