This is a post aming to show you some open source games, you can start hacking on today. I think open source games, among other things, have a huge advantage in that they probably will outlive their commercial counterparts. As the availability of many AAA games are more-or-less tied to cloud gaming platforms, it is becoming increasingly important that we have these alternatives.

Below you'll find some of my favorites. Maybe you already know them? If you're working on your own game and/or looking for contributions, feel free to add it in the comments.

Elite/Privateer Clones

Oolite: http://www.oolite.org/
Pioneer: https://pioneerspacesim.net/

Endless Sky

https://endless-sky.github.io/

The Battle for Westnoth

https://wesnoth.org/

Chocolate Doom

https://www.chocolate-doom.org/wiki/index.php/Chocolate_Doom

Civilization

http://www.freeciv.org/

FreeCol

http://www.freecol.org/

Transport Tycoon

https://www.openttd.org/development.html

Xonotic

https://www.xonotic.org/
(Gitlab link at the bottom of the page)

SuperTuxKart

https://supertuxkart.net/Main_Page

Fellow dev.to user Thamara Andrade has made a great article on how to contribute to Open Source, you can find it here:
https://dev.to/thamara/contributing-to-open-source-a-brief-how-to-i36

Wikipedia is a great source: https://en.wikipedia.org/wiki/List_of_open-source_video_games