I didn’t see anyone mention Warzone2100 yet. An excellent RTS, with a neat research system and unit customisation, and fun campaign. They’ve recently added a couple of new campaigns I haven’t played yet, and have enough ongoing dev work on skirmish/multiplayer that some AIs are listed as “X% win rate in AI matches”.
Super Tux Kart (I play it on Android) is NOT one of them. The physics system is bad at some moments, the items aren’t fun to use and some of them ruin the game. The overall game feels amateurish (in a bad way), but one thing that I like is the Windows Car and the drifting. Those are awesome.
Open source is not the same as source available. I’m not going to do a deep dive on definitions and licensing, but open source generally means that you are allowed to do what you want with it. It also usually implies that if the creator updates it, that updated code will also be shared.
The leaked Cyberpunk 2077 source code is from 2022 at the absolute latest (released 2024 from a hack done in 2022), is not open source licensed for re-use (meaning any use of it by people outside of CDPR is illegal), and they have released numerous patches, updates, and an entire DLC since.
VCMI - it’s re-written from scratch, open source, multiplatform Heroes 3 engine with many improvements and mods manager. It requires some files from the original game though.
It’s definitely a work-in-progress title, but I have really enjoyed SuperTux Advance (AGPL-3.0 according to their github page). It’s like SuperTux but with sliding, more playable characters, and more power ups. As of now it’s probably my favorite OS game at the moment. -Ace
CrossCode is really good, but it isn’t free. I need to look through my Steam library to see which other games might be open source too. This is the only one I’m aware of, really. ProtonDB might have a list of games that are open source. It’s a great resource for checking compatibility if you’re playing on Linux.