I can literally explain the rules right here and now, actually. It's that rules-light (excluding the Risus Companion, a 40 page supplement to a 4 page core book.)
Risus for all y'all newbies:
First things first, Risus only uses regular six-sided dice. Secondly, there are no classes and levels; you have ten dice to assign to "Cliches", which are basically character classes. They can be literally anything you want, as long as it fits the context and setting (some GMs disregard this entirely).
Example character: (This is the character sheet too. You can post your sheets right now if you'd like.)
Name: Willie the Punk
Description: An avid driver, drinker and roughhouser, Willie is a tough nut in an apocalyptic sea of nails. A freelancer merc, Willie is in command of a "remodified" (by remodified, we stuck spikes on with ducktape) SUV, hoping one day to earn enough bottlecaps to open his one hair salon. (Mohawks for all!)
Cliches: (He has 10 dice to spend on as many cliches as he wants. It's not recommended to spread out and put one dice in ten Cliches, for example; you'd suck at everything. You don't need a cliche to do an action anyway. Explained later.)
(4) Wasteland Brawler
(3) Wasteland Driver
(2) Punk Barber
(1) Apocalyptic Survivor
(By the way, the most you're allowed to allocate into a Cliche is four at the start, most of the time. I'm using those rules for this game.)
Whenever you need to do an action, you roll dice equivalent to your Cliche that you specify. Example: The mutant bandits are catching up fast on their bikes. Willie uses his Wasteland Driver (3) to use the barren wasted terrain to shake them off. He rolls three dice and ends up with 15, while the GM rolls for the Loud Bikers (4) who roll 13. Caught up in the brazenly loud rumbling of their bikes, they don't hear their leaders warnings as Willie turns a corner and they crash into a wall. Rolls that aren't contested, such as picking a lock, will have a difficulty set by the GM:
5 for easy stuff. Pretty hard for normal dudes (but you ain't normal).
10 for challenging stuff. Most things will have difficulty 10.
15 for pretty heroic stuff. Whenever you try something daring or stunty.
20 for really heroic stuff. Firing a pistol at a target two hundred meters away.
30 for impossible stuff. Firing a pistol at a target two hundred meters away. Blind. With your feet. Handcuffed.
Now, combat in Risus isn't always the regular RPG combat you're used to. It doesn't necessarily imply violence, fighting or even attacking. There is, of course, brawling and physical and magical combat, but there's also "combat" during courtroom hearings, yo mamma contests and even origami contests. The duration of combat could last seconds between turns, hours, days or years. All is up to the context, the players and the GM.
When you are in combat, you roll your cliche's dice against the enemy's. Every time you beat their roll, they lose a dice in that cliche and vice versa. When you lose all dice in a cliche, you lose. Even if you have other dice in other cliches. The winner determines the losers fate, which can be literally anything (within reason, but screw reason). An example straight from the rulebook: Bob wins a tennis match against Chester. Bob drags his opponents corpse victoriously across the streets for three days. (Now, I probably won't let stuff that drastic be allowed unless you give really good roleplaying or detail it in a really funny way).
In combat, you can use Inappropriate Cliches, which basically are anything that wouldn't make sense fighting the enemy in that type of combat. Imagine a wizard duel: Azaron the Multi-hued is challenged by the newcomer, Bob the Homicidal Tennis Player. Now see, it is a wizard duel, so Tennis Player is the Inappropriate Cliche. If it were swapped, and Azaron was challenged to a game of tennis (call the cops now) then Azaron's Rainbow Wizard would be the Inappropriate Cliche. Combat is like usual, but if Bob's dice roll beats Azaron's, then Azaron loses three dice instead of one. Bob would only lose one if he lost. This encourages thinking outside the box.
Finally, there are teams. Grunt squads and PC teams. Grunt squads are so the GM doesn't have to keep track of 3000 orcs and roll 3000 times. Instead, he can put them into a grunt squad (or multiple grunt squads) to make them easier to manage and to attack. The individual 3000 Orcs (1) are now ten squads of 300 Orcs (3). That's still a lot of squads, but you get the gist. PC teams are comprised of PCs and sometimes NPCs. The team's leader is the one with the highest-ranking applicable cliche and use the team leader's cliche when rolling. Everyone else in the team rolls their dice as well, but only adds their sixes if they have any. When a PC team loses combat, either the Team Leader assigns the damage to a teammate of their choosing, or someone (including the Team Leader) can step forward and choose to lose TWO dice from their cliche, and the next round the Team Leader can roll TWICE as many dice.
I think that's it. The rulebook has a bit more things in it, along with a bunch of stick figure drawings, but this is more than enough to play. Anymore questions, just ask.