0 A.D has been very fun, although I play offline because I’m casual af :) Has all the things I liked about Age of Empires and more, and I’ve been building from source so it gets improvements every week.
Xonotic has had an excellent community whenever I’ve gone online, so can recommend.
If we just talk about the last few years:
There is a soft spot in my heart for SuperTuxKart too, despite the current project leadership.