Rock paper scissors

Press the button and get rock, paper or scissors, each exactly a third of the time. Use it to settle something, or to practise against an opponent with no habits to exploit.

Against a uniformly random opponent no strategy has an edge — whatever you throw, you win a third, lose a third and draw a third. That sounds like it makes the game pointless and it is actually the reason to use this: human rock paper scissors is a game of reading habits, and people have plenty. Men open with rock noticeably more often than chance; players who just lost tend to switch, and players who just won tend to repeat. World-championship play is entirely about exploiting those tendencies. A random throw has none of them, which is what makes it the fair way to settle something rather than a way to win.