Did you get a little worried at the start of that headline? Fret not, as it's about the game 'The End Is Nigh' and it's now out of beta on Steam for Linux.
Need a super cheap time filler? Grass Cutter seems like a reasonable game to add to your backlog that has Linux support. It seems totally silly, but it's actually not bad at all.
Do you like survival games, how about one that has both a single-player story and a general survive mode? The Long Dark might be what you need and it continues to get better.