This one is rather specific, but a game rhythm based Final Fantasy game called Theatrhythm Final Bar Line is simply not allowing people to play today because it has an internal system that awards prizes for specific days and they didn't handle the case of what to do when it's on a leap day. You can boot it up but can't actually play the game as a result.

Not working on the game or anything but found it moderately amusing as someone who owns the game!