Freespace 2 comes to mind. The whole game engine was open source not just the game itself. Looks like there is still a community building on it too. https://scp.indiegames.us/

Thanks for the post! I just picked up the full bundle myself. Hopefully, I’ll get further than the time I was playing with unity. Lol.

1961 Gibson Discoverer Amp. Found it in the basement as a teen. Replaced the fuse holder and fuse. Powered up all the tubes no problem and still running strong today.