From the campaign:
Yarr! is meant to be accessible and fast and more narrative than crunchy. I know people will houserule what they want to, and I actually encourage it in the intro!
Yarr’s game mechanics are based on Swords & Wizardry but translated into to five pirate classes. There are no ability scores (of course that would be very easy to put back) and rolls to achieve actions are basically all saving throws except combat and class skills. Class skills are really old school: a chance on 1d6 (for example, hide in shadows 1-3 on 1d6). PCs are limited to a maximum level of 5, but there are other ways to advance after 5th level.
One thing that's a little unique is the ship to ship combat which I like to think is pretty clever; realistic enough but not so complex that it takes an hour to do one broadside. There are optional rules to add more crunch for skills (these rules borrow the Prime concept from C&C, sort of) and some extra optional crunch for ship combat.
The Kickstarter is about 3/4 of the way to their goal, but there's only 5 days left to get in on it if you want.