I mean there is the classic GZDoom + Freedoom

Work in progress: https://libla.st/

I've played a lot of Xonotic in my day.

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.

It's got active servers, even.

Does open arena, red eclipse 2 and warfork count?

Sauerbraten.

There are always some players on Venice map.

Warsow / warfork

https://warfork.com/

Cube 2: Sauerbraten seems to still be maintained. I haven't played it for a long time, though.

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

Can I add that I'd like to know if they're PvP or story driven. I'm only interested in the second.

There was IW4X. GPLv3, I believe.

etlegacy... the best.

Warfork

OpenArena