Free Systems

Animaloid
A Samurai Pizza Cats roleplaying game.
http://www.geocities.com/Tokyo/Towers/9607/animaloid.html

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.
http://appleseedd6.tripod.com/

The Free Anime Role-Playing System
A simple system for tabletop or IRC use.
http://www.geocities.com/Area51/Corridor/4286/farps.html

The Nexus
A companion site to Thrash RPG. Currently features only a Thrash Martial Arts Compendium, but there are plans for further addition.
http://www.angelfire.com/scifi/scarlet/

Whimsical Orange Road
Based on Izumi Matsumoto's Kimagure Orange Road anime and manga.
http://www.geocities.com/Area51/Corridor/4286/korrpg.txt