Interaction Design Photoshop from IDEO
Avocado is the open-source user experience prototyping tool. It builds on the functionality of Origami, a similar tool released few months ago by Facebook. IDEO built Avocado for their designers so they could rapidly prototype interfaces using Lego-like blocks. With this software you will be able to create detailed, full-motion mockup of how an interface of your future app could work.