UI Sketcher from Box UK isn't just another sketching app for the iPad. It's based on principles followed by user interface experts and includes tools to help you quickly capture your initial thoughts in sketches, then develop those ideas into UI mock-ups you can share with colleagues and clients.

UI Sketcher's pen palette, which you summon with a three-finger tap on the iPad, holds five drawing tools:

You can begin sketching on a six-up template and refine sketches in a a one-up template. To zoom into your work, use a two-finger pinch.

To make it easier for you to share sketches with others, UI Sketcher integrates with email and Dropbox.

The app costs just $3.99 and is compatible with the iPad 1 and 2 running iOS 3.2 and later.