Does anyone know any open source FPS still maintained? I know some like Unvanquished and Xonotic and they are ok but I would like to know some others, if they exist.
They are on Codeberg, which is a much more vibrant FOSS community than Github. I highly doubt being on Github has any sort of benefit for these kind of non-corporate projects. It would be probably detrimental as many FOSS enthusiasts refuse to use Github.
When I played regularly, it was mostly back before Xonotic was renamed/forked from Nexuiz. But it's a great game. Similar to Quake 3. It's built on a customized and modernized fork of Quake 1.
Know what would be interesting? If Valve released the code of CS1.6 for free and the required tooling. For what's worth I believe large portions of that was already leaked or at least reverse engineered.
Red Eclipse 2 was mentioned but it’s a great example. Using the same engine and hasn’t had a release since 2021 is Assault Cube Reloaded. https://github.com/acreloaded/acr
I just tried it and I love it, I have absolutely nothing against the other recommended games but I'm more player Battlefield-type FPS and this is just awesome, thank you!