Risus is a fantastic "generic" RPG by S. John Ross, A True Legend and Genius (6).
The core mechanic is simple - characters are built using Cliches. These are short, descriptive phrases that sum an an aspect of a character (so, Down on His Luck Private Eye, Terrifyingly Naked Barbarian Warrior, Green-Skinned Space Babe Looking For This Earth Emotion You Call "Love"). You assign a number of dice (plain old d6) to each Cliche - up to 6, for world-class ability in the field, to one for utter crap.
You can use your Cliche wherever it seems appropriate - so, you could roll Down on His Luck Private Eye for investigation, fending off a Femme Fatale's charms, or knowing the cheapest bars in town.
Risus is a game about conflict at its heart - but that's not strictly combat.
You can roll your Cliche dice against a static Target Number - score more than that, and you've managed it. So, climbing a wall (easy for a Cat Burglar, hard for a Parapalegic Private Investigator), finding the right piece of information - something simple and with no-one actively trying to stop you.
You could face off against someone in a one-shot conflict - an Opposed Cliche Roll (both roll your cliches, highest total wins). Good for brief contests (like arm wrestling, or a quick-draw).
Or, you can go for a full-on combat - players roll their Cliches, the loser drops a dice off their Cliche total until someone has no dice left. Good for full-on contest with multiple actions (like a fight, where someone can throw a few good punches, then lose their footing, or get pummeled in return).
But, you can use those three systems to run anything - lets try... an argument.
If the players want it to be over quickly (or it would be pointless to actually roll, like a Deviously Charming Mastermind (6) rolling against a Simple-Minded Obedient Minion (2), you could use the Target Number - a nice low one, as talking down to Minions is what a Mastermind does best.
Or it could be a Contested roll - there's far more chance of the Mastermind winning, but it gives a higher chance of failure as well. Good if there would be consequences to failing (like having to give out a pay rise to his Featurless Goons).
Or, lastly, it could be a full combat - attempting to run rings around each other, trying to get the opposition to slip up, trying various gambits and tricks to get your point across. Best if the players can really give a good explanation of what they're trying, and you're willing to improvise some good failures for the NPC.
It's also fun to take simple things and make them into long, extended battles - like the Arm Wrestle, with each dice lost representing distractions, tricks and subterfuge, and the occasional reserve of strength being broken out.
Really, that's it. The basics are out there, and they're even more entertainingly explained in the Rules. Download them from the top of the page. Go on, I'll be waiting.
And now you're back, go download the Risus Companion. For the princely sum of $10 (or, for those of us who use the Great British Pound Sterling, just a touch over £6), you get not only a 64-page instruction manual for a 6-page free RPG, you also get membership to the International Order of Risus. You get a card, and everything (and chicks really dig the card).
Check out Risus Monkey's Love Letter To The Companion for a far better explanation of the joys within than I could ever manage.