We survey research on multi-user brain-computer interfacing applications and look in particular at 'multi-brain games'. That is, games where in one or other form the (EEG-) measured brain activity of more than one user is needed to play the game. Various ways of integrating and merging brain activity in a game context are investigated. Existing research games are mentioned, but the emphasis is on surveying BCI research that will provide ideas for future multi-brain BCI games.