more work

https://sourceforge.net/p/uhexen2/code/HEAD/tree/ Hexen II: Hammer of Thyrion
http://hgm.nubati.net/ (winboard)
http://insideastarfilledsky.net/ (source may be somewhere else)
https://empiredirectory.net/
https://empiredirectory.net/index.php/downloads/viewdownload/6-server-software/13-empire-server
http://www.divgo.net/ (in spanish difficult to detect sources)
https://github.com/neuromancer/re-private-eye.git (moved to scummvm) and is part of scummvm
http://www.hard-light.net/ (Free Space Open, Knossos, Mods, https://github.com/scp-fs2open/fs2open.github.com, https://wiki.hard-light.net/index.php/Getting_started)
http://svn.assembla.com/svn/gdpl/ (not sure what links there and what kind of game it is, license?)
https://web.archive.org/web/20161230103538/http://www.linuxdevcenter.com/pub/a/linux/2003/04/24/exult.html
http://barbarian.1987.free.fr/indexEN.htm (many version, source license?)
https://github.com/Warsow, https://www.warsow.net/ (what part of it is open source and what is not?)

roguelike

http://web.archive.org/web/20071218214256/http://users.tkk.fi/~eye/roguelike/nethack.html
http://www.dungeoncrawl.org/?d.l

multiple

http://androidsoft.org/
http://antongerdelan.net/blog/ (other projects besides TestDrive)
http://e-adventure.e-ucm.es/login/index.php (games of eAdventure)
http://hcsoftware.sourceforge.net/jason-rohrer/ (split games there)
http://lukaszjakowski.pl/ (games apart from uMario)
http://media.pyweek.org/dl/7/ (all of them)
http://stage.gamecreation.org/ (all of them)
http://stellarengine.nongnu.org/games.html (all the games)
http://wiki.gp2x.org/articles/g/a/m/Category:Games.html (all of them)
http://wiki.scummvm.org/index.php/HOWTO-Fangames
http://www.finkproject.org/index.php?phpLang=en (do they have games)
http://www.ossblog.org/fun-play-open-source-turn-based-strategy-games/ (and others there)
https://archive.org/details/Gna_code_hosting (all of them)
https://awesomeopensource.com/categories/games
https://awesomeopensource.com/projects/strategy-game (and others there)
https://awesomeopensource.com/projects/strategy/turn-based (and others there)
https://directory.fsf.org/wiki/Collection:GNOME_Games (all of them)
https://dosgames.com/about.php (search for public domain games with sources)
https://drodin.com/ (all games there)
https://fede0d.github.io/games/ (all of them)
https://faq.tuxfamily.org/Games/En
https://flathub.org/apps/category/Game
https://fydo.net/projects/island-rescue (and other projects there)
https://gamejolt.com/ (search there)
https://games.kde.org/ (all of them)
https://games.kde.org/old/kde_arcade.php
https://freegamer.blogspot.com (maybe there is something interesting)
https://github.com/cymonsgames/CymonsGames (collection)
https://github.com/grantjenks/free-python-games (check all)
https://github.com/OSSGames (all there, but we should have them already)
https://jotd.pagesperso-orange.fr/ (several games)
https://kde.org/applications/games/ (all of them)
https://opensourcesoftwaredirectory.com/Games/Strategy-games (and all others there)
https://opensourcesoftwaredirectory.com/games/strategy-games (and others there)
https://projects.tuxfamily.org/ (all of them)
https://www.tuxfamily.org/ (if there are games)
https://repology.org/ (for looking up other repositories of games)
https://sites.google.com/site/syllablesoftware/games (List of games (with screenshots) that have been ported to Syllable OS)
https://sourceforge.net/directory/games/games/os:windows/
https://sourceforge.net/directory/games/turnbasedstrategy/ (and the general games directory, maybe even sourceforge metadata, see https://github.com/chpwssn/sourceforge-items, https://github.com/JesseWeinstein/sourceforge-items-cache)
https://stabyourself.net/ (all projects there)
https://stephensmith.itch.io/ (all of them)
https://tangramgames.dk/games/ (all)
https://wiki.debian.org/Games/Unsuitable
https://www.allegro.cc/depot/strategy/ (and all other genres there)
https://www.gamingonlinux.com/free-games/ (all of them that are open source)
https://www.gog.com/forum/general/free_open_source_games (and suggestions therein)
https://www.openhub.net/ (search for games)
https://www.reddit.com/r/opensource/comments/cs6m3y/a_list_of_fossrelated_projects_people_to_follow/
https://www.reddit.com/r/opensourcegames/
https://www.renpy.org/ (also all projects linked there)
https://gottcode.org/ (all)
https://love2d.org/forums/viewforum.php?f=14 (check them if time)
http://www.linux-games.com/ (all there)
http://www.newbreedsoftware.com/ (all)
http://www.computerchess.org.uk/ccrl/4040/rating_list_all.html
https://appimage.github.io/categories/Game
https://edu.kde.org/
https://fedoraproject.org/wiki/SIGs/Games#List_of_games_we_will_NOT_package
https://forum.freegamedev.net/viewtopic.php?f=20&t=11627
https://forums.scummvm.org/viewtopic.php?t=13512&highlight=open+source
https://invent.kde.org/games
https://itch.io/ (scrape, look for open source)
https://lmemsm.dreamwidth.org/8013.html (List of some of my favorite Open Source games)
https://notabug.org/Calinou/awesome-gamedev#games
https://sr.ht/projects?search=%23game
https://www.fandom.com/topics/games (look for media links, example https://creatures.fandom.com/wiki/Openc2e)
https://www.fosshub.com/about.html
https://www.fosslinux.com/
https://www.freegamesutopia.com/
https://arcade.academy/
https://blends.debian.org/games/tasks/
https://blends.debian.org/games/tasks/racing
http://www.goldenstudios.or.id/products/games/index.php
http://www.goldenstudios.or.id/products/GTGE/
https://gitorious.org/index-list.html (are there other interesting games)
http://www.dianneandpaul.net/CSBwin/
http://www.lesfleursdunormal.fr/static/informatique/old/index_en.html
http://www.oletus.fi/games/
http://www.paulscode.com/games/

github collections

https://github.com/collections
https://github.com/collections/game-engines (only OS)
https://github.com/collections/javascript-game-engines (only OS)
https://github.com/collections/pixel-art-tools (tools)
https://github.com/collections/productivity-tools (maybe for statistical purposes)
https://github.com/collections/software-development-tools (maybe we can apply some of them across the board)
https://github.com/collections/tools-for-open-source (maybe we can apply some)
https://github.com/collections/web-games (only OS)
https://github.com/flathub (all repositories which are games there)

wikipedia

https://en.wikipedia.org/wiki/Category:Open-source_video_games (all of them)
https://en.wikipedia.org/wiki/GNOME_Games_Collection
https://en.wikipedia.org/wiki/List_of_commercial_video_games_released_as_freeware
https://en.wikipedia.org/wiki/List_of_commercial_video_games_with_available_source_code
https://en.wikipedia.org/wiki/List_of_cult_video_games (all of them)
https://en.wikipedia.org/wiki/List_of_free_and_open-source_Android_applications#Games
https://en.wikipedia.org/wiki/MUD#Spread (all there)
https://en.wikipedia.org/wiki/MUD_client (all there)

osdn

https://osdn.net/

special

https://alternativeto.net/ (query with only open source as option)
http://www.happypenguin.org (linux game tomb)
https://web.archive.org/web/20121010121342/http://www.happypenguin.org/list?sort=title
https://www.ifwiki.org/index.php/Main_Page (is there software contained or contents with CC license maybe that could be converted...)
https://web.archive.org/web/20161215063433/http://www.linuxdevcenter.com/topics/linux/games

github topics

https://github.com/topics/game-engine (etc.)