One of the best RPG systems I've ever played was the one used in RuneQuest. This was back when Advanced Dungeons and Dragons (first edition) was king, when a house cat could kill your first level character, but your high-level character could walk off a sixty-foot cliff and know he'd survive. (Okay, well, it's still sorta like that.) RuneQuest's elegant advancement system, simple yet realistic combat system, and interesting magic system made for a great little game, and the improvements to the Dungeons and Dragons second edition seemed to borrow a lot of its game mechanic ideas. Like the d20 system, the early RuneQuest system proved to be adaptable to multiple game world settings, with its core rule system used in StormBringer, ElfQuest, and the critically acclaimed and still-going-strong Call of Cthulhu.
Well, now, Mongoose Publishing is releasing a new version of RuneQuest, and it's available for pre-order now at Amazon for $19.95. More companion rulebooks are slated to follow, including a massive guide to Glorantha, the original game world setting that was so popular.
Interestingly, they're releasing it under the same philosophy as the OGL that Wizards is releasing the d20 rules system under. Although I haven't perused the license agreement, from what I've read, it's similar to the OGL in that it allows people to freely publish content for the game so long as they do it with their own IP. Nice.