Wikipedia has a list: https://en.wikipedia.org/wiki/List_of_commercial_video_games...

NOLF: https://github.com/osgcc/no-one-lives-forever

That's really cool. Kotaku ran an article <a year ago about the licensing issues around No One Lives Forever and how it would probably never make it to Steam; I'm surprised they never mentioned that the source code has been available for 4 years, buildable by anyone.

The only one off the top of my head is Serious Sam: https://github.com/Croteam-official/Serious-Engine

Marathon: http://infinitysource.bungie.org/

SoftDorothy: https://github.com/softdorothy

I wish there were more.

Edit:

Abuse: http://abuse.zoy.org/

It was so rare back in the day that I vividly remember games that did actually go open source.

Oh, Abuse. I loved this game. It was also my first encounter with Lisp, many years before I learned how it's called and what it is.

I guess part of the problem is that most producers don't want to open-source a game until it's stopped making significant money, and most games are largely forgotten by that time, so there's less incentive to bother in the first place, and (perhaps more importantly) no press when it does happen. (That Wikipedia article is surprisingly long, but I haven't heard of most of the entries.)

FreeSpace 2 -- http://scp.indiegames.us/. It got seriously remastered thanks to that.

id software followed up with lots. quake and enemy territory were amazing.

we played hours and hours every week of enemy territory in the office in 2007-2009

... on Linux (and the occasional Windows and Mac in the same server) no less!