Crystal Clear, in which the object is to blow up crystals, and has maybe one player in the lobby ever (and I suspect they're a bot).
Quadradius is checkers in some needlessly robotic dystopic future. It's the kind of video game people in Firefly would play if they ever played video games.
Both are free, but have hardly any players. You can choose to pay to play either of them if you want to, I guess.