Animaloid
A Samurai Pizza Cats roleplaying game.
Appleseed
Game set in the world of Masamune Shirow's Appleseed series using a d6 system. Sites includes game mechanics, character information, and rule book entries for: attributes and skills; actions and combat; cybernectics; and equipment.
Dojos and Dragons
A free system trying to capture the 'feel' of martial arts/comedy anime shows.
Official Thrash Home Page
A free RPG based on anime-style martial arts.
The Free Anime Role-Playing System
A simple system for tabletop or IRC use.
The Nexus
A companion site to Thrash RPG. Currently features only a Thrash Martial Arts Compendium, but there are plans for further addition.
Whimsical Orange Road
Based on Izumi Matsumoto's Kimagure Orange Road anime and manga.