Poor Theater and Theater of the Oppressed were two sort of concurrent movements that shared some of the same aims. Jerzy Grotowski's Poor Theater eschewed the use of lighting, props, costumes, makeup, and many of the other trappings of "rich" theater. Augusto Boal's Theater of the Oppressed in Brazil challenged the ideas of how plays were written and performed, and blurred the lines between actors and audiences.
Theatre of Cruelty
I don't mean it mean, but today we're going to be cruel. It's the fun-loving Theater of Cruelty, which was pioneered by the genius Antonin Artaud in France during the inter-war period in twentieth century. The Theater of Cruelty was meant to force an audience into looking at the ridiculous illusions of their bourgeois lives. Is it entertaining? Not always. Was it hugely influential? Absolutely.