For those of you who love your idle/clicker games, you might want to take a look at Chicken Assassin: Reloaded as it now has official Linux support, it seems quite popular too.
In Master Pyrox Wizard Smackdown, you face off against up to eight other wizards in small arenas. It has support for single-player against the AI, local co-op and online play too.
Doom, the classic first-person shooter has a huge modding community and it's incredible to see what people make. The latest I came across is a nonviolent mod named Mr. Friendly.
Farm Together is a really sweet and simple farming sim from Milkstone Studios that I've been really impressed with, it's expanded a lot during Early Access too.