It's also worth noting that the launch of Briefs on the Mac App Store is the end of a long and winding road for developer Rob Rhyne. I first saw a version of Briefs demoed at the C4 conference in Chicago in 2009, where it had been designed to run on the iPhone itself (no Mac app involved). Unfortunately, the project ran afoul of some of Apple's App Store rules, and Rhyne was forced to take it back to the drawing board.
There's no question that Briefs is an ambitious tool, and a professional one--at $200, it's not really targeted at the casual hobbyist. But it fills a very specific niche in design and prototyping, one that is often overlooked in the development process.
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