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.