I really liked ReBirth from Propellerheads back in the 90ies. However, I have not heard much of ReBirth (and of the good old Roland 303 and its companions) since then. Now, ReBirth is back on the iPad (although there is also an iPhone/iPod Touch version of it only the iPad version seems just right) and it feels just like a flashback to the old times. Astonishingly, the sound of ReBirth is still fresh.
Anyway, I really like the way in which the video aboce outlines the functionality or the rather complicated synthesizer touch GUI.