The Barbarians of Lemuria system* by Simon Washbourne is easily converted to other genres. What follows are a few of the published variants.
Barbarians of Lemuria Legendary (the advanced rules) uses a Lemuria of Washbourne’s devising since he was unable to acquire the rights to Lin Carter’s version of Lemuria (used with the free version of BoL).
Barbarians of the Aftermath is a post-apocalyptic setting which provides additional Careers, rules for “build-your-own” apocalypse, vehicle rules, and so on.
Dogs of W*A*R is Washbourne’s rules for the Big Muscles, Big Guns books and movies of the 70s and 80s ala A-Team, Mack Bolan, and others.
Legends of Steel (BoL version) is another setting using these rules.
Dicey Tales (a PDF magazine) has rules for Pulp-styled settings.
Honor + Intrigue is a swashbuckling set of rules combining BoL with a bit of 7th Sea and a dash of the action breakdown of Dungeons & Dragons 3rd edition. This system tends to stretch the basic BoL system enough that it’s almost a different game, but I am still interested in running a campaign using it.
Barbarians of Heavy Metal is a Kickstarter using the BoL (and Barbarians of the Aftermath) rules tweaked to represent the Rocktagon: the Eight Great Schools of Rock as the characters wander the desolate wastes seeking fame and fortune. I’m interested in seeing what the author has come up with for this game.
Those are the settings I have come across. If you’ve come across others, let me know.
*Often referred to as the BoX system.