Questions, bug reports or ideas: email aiqbltd1@gmail.com. Please say which app and which iPhone you are using.
Rematch: Two Player Games. Two players share one phone, sitting face to face. Each player's controls are at their own end of the screen. Every game works on any iPhone. On iPhone Duo, lay the phone flat between you; closing it pauses the game.
Music Stand. Add scores from Files, Safari or Mail ("Open in Music Stand"). Your library is in the Files app under Music Stand, so it can be backed up. On iPhone Duo, open the phone to see two pages side by side.
Gambit: Chess Clock. Tap your own side of the clock to end your move. For 3 to 6 players, lay the phone in the middle of the table.