A neat feature of the Barbarians of Lemuria RPG system is the way it handles character "class" and skills. Being based on a setting that centers on a Conan-inspired "a thief, a reaver, a slayer"-type polymath-hero, the player characters in Barbarians of Lemuria can take on multiple character archetypes, each with a nebulous (and open-ended) set of skills and abilities that replace an otherwise exhaustive set of skill lists and character "feats".
The system handles this without it being tied to combat, as Combat Abilities (Brawling, Melee, Range and Defence) are their own set of stats.
For example, as a Thief, you can attempt things a generic fantasy Rogue can do, like sneak around, pick-pockets, deal with traps, pick locks, and if you are a creative player (as people are too spoiled on what a D&D Thief/Rogue can do), you can also play as a con-artist (assets marks, bribe/blackmail people, fake magic-use, etc.). As a Barbarian, you have tracking/survival, intimidation, primal instincts, raw sexual magnesium, cool one-liners, etc. Even something as weak and humble as a Slave or Beggar could have a lot of benefit to go with it as both, for example, can move unseen in crowds and pickup a lot of gossip. Some may even have exclusive abilities.
To do this, Mutant Lords should make-up a list of Careers/Archetypes (which ever you choose to call them) for the players to choose from, to help define their characters. Players should choose the first one define their character's background (like Beggar, Farmer, Barbarian, Slave, etc.), then choose one or more that defines their character currently. With each Career, the ML chooses what if they would have a target number, ether set to a fixed score (like with Saving Throws), or rolled individually (3d6, lower the better). When a player attempts something a Career can handle, roll a d20 equal or higher than the target number to succeed at the task. Careers maybe tied to one or more ability scores, with high and low scores effecting the roll. Advancement can lower the target number, ether by a fixed amount (like for the fixed score), or with a die roll (1d3 or 1d4 with individually rolled scores).
Being a science-fantasy setting were civilization is in a near-barbaric state, MF has meany archetypes found in low fantasy (or high if you allow for magic) and the pulpy side of science fiction.