The iPhone version of Sunrizer is free! There are no details on why it is free today, or how long it will stay free, so grab it now!
Even if you don't have an iPhone, you may one day and on that day you will deeply regret not having this impressive synth. It is unique among the subtractive synth apps, with a morphing engine to glide between different patches as you play. If you don't already have it for the iPad (link to review), consider this a demo!