Rock paper scissors
Tap the button and the app throws rock, paper or scissors. Play against it, or let two people each tap once and compare.
Rock beats scissors, scissors beats paper and paper beats rock. Each throw is independent, so there is no pattern to exploit.
Questions
Is the computer's throw random?
Yes. Each throw has an equal 1 in 3 chance and does not depend on earlier throws.
Can I add lizard and Spock?
Yes. Edit the list from the ⋮ menu and add them.