OpenRPG
From Exalted - Unofficial Wiki
Open source on-line roleplaying application. It is an IRC-like application written in Python to facilitate roleplaying on the Internet. In addition to having an advanced dieroller, it also has a map, a node tree (often used for character sheets), and a standalone server. Being Open Source, you can also extend both the server and the client to give them additional capabilities, though I don't know of anyone but me who has modified the 'official' server code outside of the actual development branch.
A number of Exalted campaigns currently run on it (at least a dozen, by my count).
