Basic Fantasy is a free RPG system, complete with dozens of modules and supplements. The author writes:
The Basic Fantasy Role-Playing Game is a rules-light game system based on the d20 SRD v3.5, but heavily rewritten with inspiration from early role-playing game systems. It is intended for those who are fans of “oldschool” game mechanics. Basic Fantasy RPG is simple enough for children in perhaps second or third grade to play, yet still has enough depth for adults as well.
This is a major work.