The Constantly Altering Law-Variation and Innovative Nonsense core ruleset (aka CALVIN Core) is a simple tabletop roleplaying game system that can be played on its own or used as the basis for creating your own game.

As its (rather long) name suggests, it’s a very silly ruleset that starts simple and then transmogrifies into something far more ridiculous as the game goes on!

Thanks to Lex Kim Bobrow (@titanomachyRPG) for the wonderful, and far more sensible, inspiration that is Caltrop Core.