I'm currently reading through RuneQuest 6. One of the things that initially drew me to RuneQuest is that I've always heard that its advancement system is organic, where advancing a skill is accomplished by using it—something like, when a skill is used it's checkmarked, and at the end of a session/adventure you test each checked skill to see if it increases. Ironically, I now know this has been removed from RQ6 and replaced with what's effectively an experience point mechanic.
I'd like to know which edition or editions do use the organic advancement method I keep hearing about, so I could get a copy to evaluate it for porting into RQ6, which is otherwise very much to my taste. It's unfortunately not as simple as just implementing the brief outline I gave above, because the new XP system hooks into other parts of character improvement that don't have obvious organic-advancement replacements.
I've looked at OpenQuest and Runic SRD (Mongoose RuneQuest II / Mongoose Legend), but those skill advancement systems are nearly identical to RQ6.