… is a nifty HTML5 App used to create wireframes, mockups or UI concepts, prototypes depending on how you like to call them.

… wireframing, mockups and prototyping for websites and applications

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.

Download the desktop version of Balsamiq. Works offline, one-time purchase.