You might want to look up PCGen. It isn't what it used to be, but it might help.
When it started, you could write custom files for races, classes, equipment, whatever. And then run PCGen, and you build your d20 character in whichever d20 game.
Hmm, come to think of it, it was stuck on requiring alingment, so maybe it's not a good idea . . . <sigh>