ChipIn is a paypal based service to help people share costs for things. They're based in Manoa valley on Oahu. Inspires me that you can do a successful startup in Hawaii! I'm proud to be starting TripInvite here, and want to help build the startup community here (as well as a world-class group travel site).
Hawaii Business Magazine had a good article about them and their startup experience.
Part 1 of the story