Looking for a ruleset

Gonna make this short...
I build Web browser RPGs and MMOs. Mostly 2d text style. I try to keep them as RPG as possible.

I have a new game design that will allow players to not only play quests/adventures but make them for other people to play also. Much like NWN but instant click and play and more text based.

What i need is a already made system. Preferably one with plenty of already made content, published or not. I would like the players to be able to download the manuals to the game so they it can be treated like a pen and paper game. Depending on the popularity of the game system and its author would get attention to their work.

I am looking for a system with a ruleset, equipment, spells/abilities, ect.. already made or in the process of being made. It takes long enough to code the game let alone have to write a system and balance it.

Thanks....