From the introduction:
"Mecha" is the term used by Japanese animators and fans to refer to the mechanical designs that appear in Japanese animation, or anime. A mecha can be a giant robot, a suit of powered armour, or a vehicle of some other sort, such as a spaceship, tank, submarine, or motorcycle.
Mecha d20 provides a means of describing all manner of mecha in game terms, and offers simple, playable systems for using them in adventures. Although its primary focus is on anime-style giant robots and powered armour, Mecha d20 can be used to create everything from sports cars to sky galleons.