Many of the earlier roleplaying games used the Runequest system or a very close
relative that was obviously inspired by Runequest, some with official permission
like the first version of The Morrow Project, some without such a direct connec-
tion like The Expendables. In fact, there are some roleplaying "sages" who claim
that Runequest, all in all, was the most influential system ever published.
Edit.:
To give an example, this is what Ron Edwards, the author who came up with the
GNS Model of roleplaying, wrote about BRP/Runequest in his essay on simulatio-
nism:
http://www.indie-rpgs.com/articles/15/