From the website's FAQ:
What is the default setting?
The default setting is a fantasy Renaissance where magic is used for social engineering. Think Three Musketeers meets Brave New World.
What's the core mechanic?
SK uses a die-step, roll-over-target-number system. So skill checks, attack rolls, and magic rolls are all rated according to a die-size (d4, d6, d8, d10, d12, and d20). If you roll and beat the target number or your opponent's roll, then you succeed.
What's combat like?
It's kinetic. It's a little wild and hectic. And it's very, very fast.
There's no initiative. Everyone goes at once. If you can guess what your opponent is going to throw at you - a Haymaker, say, or a Trip - then you can choose your own maneuver to counter that. You're aided in your guessing because each fighting style is different in how one attack sets up the next. Knowing what style your opponent is using is quite important. Not only does an opponent's style betray his possible attacks and counters, but it also allows you to change your own style, if you know more than one.
Twin Weapon Fighting, for instance, has lots of attacks, but not a lot of penetrating power. Guardsman is a good counter-style. But if you don't know Guardsman, and you're facing a TW Fighter, then you have to make do with the different maneuvers within a style that you do know. You'll have to keep your defenses up and time your attacks to when the TW Fighter is catching his breath, finding his balance, setting up a flurry, feinting (if you can guess when it's really a feint!), or moving.