Setster

Setster is a web-based application that gives service providers and teams of  professionals the ability to accept appointments online using a widget that can be
embedded on any website. Service providers can manage their online calendars and appointment books in a very simple and intuitive user interface, while allowing their
clients access to their availability.

Here is an interesting article in FastCompany that describes our start:  http://www.fastcompany.com/blog/francisco-dao/buzz/homeless-entrepreneur-shares-office-millionaire