You can currently run sphereFACE on Windows (all versions since XP SP2), Linux (any!) and OS X (Mavericks onwards - although it may run on earlier versions). All Beta snapshots will be built for those three platforms.
Additionally, if we reach the relevant stretch goals, we'll be porting to Android phones (including VR support), IOS for Apple phones, and we're aiming at console release on PS4 and Xbox One.
But our primary development is on all platforms on the PC.