Klevgränd has released Haaze, a stereo spreading plug-in for Mac OS X, Windows and iOS in AU and VST plug-in formats.
By splitting the input signal into 16 different frequency regions, spanning from 20 Hz to 20kHz, Haaze can add different amounts of stereo-widening to different frequency regions. This makes it possible to transform a mono track into a natural sounding stereo track (by, for example, keeping lower frequencies in mono while spreading the higher ones).
Haaze is compatible with both iPhone and iPad (AUv3), and also available for desktop as AudioUnit and VST.
With an intro price (~35% off) Haaze for iOS costs $4.99 and Haaze for desktop costs $12.99.
Klevgränd has also made the iOS version of Svep free.