From the Zarrakan Website:
Zarrakan is my main concentration, and thus what I'm best at, but I have also learned how to run Palladium Books' Systems Failure, Risus: The Anything RPG, Steve Jackson's Munchkin card game, White Wolf's Changeling: The Dreaming, Vampire: The Dark Ages, Vampire: The Masquerade, and Werewolf: The Apocalypse. Later on as I start to read the rules for the various RPGs and board/card games I've collected over the years I'll be able to GM those as well. Interestingly enough, I still don't know how to run Dungeons and Dragons even though it was the first tabletop RPG I ever played. =)
Of course, beyond being able to run Role-Playing Games, I'm also a Role-Playing Game designer through my efforts with Zarrakan. As such I have an intrinsic understanding of Role-Playing Game mechanics that most GMs (Game Masters) don't have, and often use such knowledge to my advantage while running Role-Playing Games. I recommend playing Role-Playing Games run by GMs who are also Role-Playing Game designers whenever you can as they are often more fun and involving than Role-Playing Games run by other GMs.