D20 System

Red Tide MUX uses the D20 system created by Wizards of the Coast, and is presently using the latest edition of their game, freshly out in June 2008.

Concern with the D20 system is only necessary for Adventuring PCs. Background PCs are intended for light roleplay and casual interactions that don't require game systems to describe, and can simply be roleplayed without reference to the the game mechanics.