Unvanquished is an open-source FPS game featuring team-based strategy and RTS elements, pitting humans against aliens in a futuristic setting.
https://forums.unvanquished.net/
I know, Unvanquished offical deleted Tremulous maps from game (but it possible download form sourceforge)
I think add-back it very good idea.
Anyone can host a server with the old maps. They may need to be upgraded slightly though, which isn't really documented much at the moment. Whoever does this should add instructions to the wiki!