BIND is an open source RPG written in LaTeX, so anyone can hack on it, add things, or rewrite the system.

(BIND stands for 'BIND is not D&D')

There's a full wiki explaining the commands.

It's designed so writing adventures is easier with the LaTeX commands. Just write \goblin and a random goblin is summoned onto the pdf, with all the stats worked out.

Currently there's an introduction adventure in the works, so if you have any idea what kinds of traps gnomes might make, or have any ideas on negotiating with a dragon, fork the book and give me a pull request.