Dustbowl Prophets

From the introduction:

Dustbowl Prophets is a serial theatre game. That is to say, it’s a regular monthly get-together where players gather, take on the roles of various characters in a fictional world, and pretend to be those people for a few hours. Prophets falls messily into an area somewhere between improv theatre and live roleplaying games. In many ways, it is a laboratory in which players are trying new ideas and half-forgotten ones for getting the kind of play that they always wanted.