- No character classes
- Low hit point accumulation (combat is deadly, experienced characters are still vulnerable)
- "Skills" as the basis for character definition (a la the skill system I found appealing in Traveller; but based on percentiles, like the thief skills in D&D). Basically anyone can learn any skill
- Advancement by improvement of skills/attributes based on use of the ability or explicit training
- Armor protects against damage
- Opponents (NPCs/"monsters") statted out in the same way as the PCs
The original game (1st and 2nd Edition) were nominally set in the world of Glorantha, which was Greg Stafford's personal fantasy world.
Through a variety of historical reasons, the RuneQuest brand moved from Chaosium. It was originally licensed to the old Avalon Hill boardgame company because they wanted to start producing RPGs.
After AH folded, there were a couple of attempts to revive the RuneQuest name, none commercially successful.
Many years later, the trademark was acquired by Greg Stafford, due to his association with the original setting world, Glorantha. He then licensed RuneQuest to Mongoose Publishing who came out with their own BRP-like variant. At that time they released an core SRD for their variant of RQ under the OGL.
After coming out with a second, improved, edition of the rules (this time with no SRD!) they lost the RuneQuest license, which was then acquired by Design Mechanism, who are (as of this writing, mid-2014) producing RuneQuest 6.
Mongoose continues to produce games using their core rule set under the Legend game system.
As of 2016 the RuneQuest name has reverted to Chaosium who are now creating versions derived from the Design Mechanism versions. Design Mechanism continues to create more or less compatible rules under the name Mythras.
It truly feels like a RuneQuest/BRP renaissance these days.