Sistema Daemon ("Daemon System") was created by a group of engineers as a mathematical system and later released by Marcelo del Debbio (a.k.a. ''Erasmus'') in a fanzine called Politropo, at Escola Politécnica (University of São Paulo), as an introduction to RPGs. The system is based in percentage (2D10 rolls).
Sistema Daemon is the most complete brazilian RPG system and is one of the most played in Brazil. This system has more than 30 supplements released and more than 500 netbooks for download.
Sistema Daemon is a free/open RPG system. But non-OGL! Daemon has it's own license: you are free to use the rules, copy, modify, and distribute them, for free or for commercial use.
All the system rules can be read in the official wiki maintained by the publisher (RPG Wiki).