I'm aware of Chess960, but this will probably never be supported on ChessMonitor for three reasons: First, Chess960 basically tries to prevent players from preparing (by having a random starting position) which does not align well with providing statistics. Second, it would require major UI and storage changes on ChessMonitor (like adding an option to select the starting position to compare games). And third, Chess960 is simply not as popular amongst non-professional chess players.