"Theremin" mode means that it responds to inclinations for pitch and volume, so that it can be controlled moving it in space, instead of using a keyboard. A bit like a Theremin, where positions of two hands from a pair of antennae is replaced by two angles.
"Keyboard" mode uses a small keyboard on the multitouch screen, with multitouch ebnabled for modulation (together with angles, in this mode). The small keyboard is made versatile for continuous or discrete control, from glissando to effects, to classic synth sounds.
A synth on an iPhone makes sense, because of the powerful control features of the device (accelerometers, great multitouch screen).
The sound quality is great, thanks to the specifications of the device.
Every preset can be saved and libraries can be created or loaded.
Still another synth on iPhone? This one is great because of several kinds of oscillators, special performance controls and sound quality.
It is in beta-testing stage, then it will be submitted to Apple for approval.
Pricing and Availability: