Wizards of the Coast has released the Game System License (GSL), their new version of their open gaming license. You can read the license and download the System Reference Document here. You’ll still need a copy of the core books to use the system, since the SRD doesn’t include rules, just references.
Now I can create the Woolietaurs (half man/half sheep).
Tags: 4e d&d, Dungeons & Dragons, GSL, Wizards of the Coast