Released for free in the Mac App Store and developed by Bonobo Labs, Unretina is an OS X utility specifically geared towards iOS designers and developers. What this app does is very simple: it provides a way to easily resize “2x” images built for the Retina Display in order to make them compatible for artworks on older Apple devices.
Unretina takes graphic files designed for the iPhone 4 and iPod touch 4th gen and resizes them to a resolution compatible with, say, the iPhone 3GS and older iPod touches. It should work for all devices that don’t come with a Retina Display. Through a simple drag & drop interface, Unretina looks like a straightforward utility for designers that does one thing well.
Looking at the reviews in the Mac App Store description page, it appears that the app uses Bicubic resampling to resize graphic files. This may lead to a tiny sharpness loss, and a few pixels off. Something that, apparently, most designers won’t care about.
Unretina is available for free in the Mac App Store.