They are actually using GRPG (the Generic RPG) (google it) i don't know if it was name ezrpg at first, but it has nothing to do with the ezrpg you will find on this website.

You can buy the GRPG from the author's site though i would advice you not to, the script is written ok, but there is no protection against XSS, and there are a lot of bug to fix...