from What is Saga?:
Saga is a role-playing system. It’s a set of rules, devoid of setting, that you can use to create and run your own games. Saga is designed to be a universal system. That is, there is no implied setting or even implied genre within Saga, though there are ways for you to customize it to your needs, tying the mechanics to the setting as you see fit.
Yes, Saga is an open source role-playing system. The entirety of this book is free, and falls under [a] Creative Commons license.