10 Tools for Rapid Prototyping
LiveView for iPhone & iPad
… a specialized remote screen viewing application intended as a tool to help designers create graphics for mobile applications, it has also proven to be useful for creating quick and dirty simulations, demos, and experience prototypes.
AppControls
… makes it easy to quickly create high-quality custom controls for your iOS apps, Mac apps and for the web.
Compass.app
compile Compass/Sass easily without resorting to command line interface — Compass.app helps designers compile stylesheets easily without resorting to command line interface. It is written in Java and works in Windows/Linux/Mac OS X.
iPlotz
… wireframing, mockups and prototyping for websites and applications
Mockingbird
Wireframes on the fly … an online tool that makes it easy for you to create, link together, preview, and share mockups of your website or application.