I’ll confess to being something of a system hoarder, if I come across a game that is marked as free then I tend to download it so that I can read it or at least be inspired by it.

There are lots of games to download, I would list them all but someone already has a compendium of Free rpgs which can be found here: The Compendium of Free Role Playing Games

My favourite free game would have to be FATE published by Evil Hat , I know it is technically a game system but you can still do a lot with it and it is very easy to build your own game world using this wonderful toolkit.

I did something similar with my Star Trek game, details can be found here and here.