Originally Posted by Blue Ghost
Oh yeah? Well I'm just a little tired of learning a new set of rules every time I go for a gaming session. I thought there might something like an open source D20 thing out there to play with casually.
There are over a dozen open source RPGs out there. D20, D&D 5e, Fate, Legends (Runequest d100), Fudge are among a few of them.
Like Aramis said System Reference Document is a key search term as well as Open Game License and Creative Commons.