Oh, the lowly d4! Second in derision only to the d12 (and those imaginary dice the d3 and d5. Pfah!).
Now these oft maligned dice, known to many as caltrops, have two games designed just for them.
Caltrops is a small supplement featuring two dice games as played by the warrior goblins of Tufartu Reach. One game is in the push-your-luck style, and the other is a betting game.
Caltrops can be used to add just a touch of flavor to your campaign, where players might run across NPCs playing the games in their travels. Or, you and your players can use the two games more actively, to settle disputes between themselves and the NPCs with flair.