From Beepstreet comes Impakton ...

Impakton turns any surface into a playable percussive instrument. You just slap your desk like a real drum, the transient acoustic signal is fed into the physical modeling engine and turned into the desired sound. That makes Impakton an extremely expressive instrument. Drop a coin on the desk, select any of the membramophones presets and you will hear the sound of the coin dancing on a membrane.

Features:

• Semi modular architecture
• Physical modeling + frequency modulation + noise shaping synthesis.
• Multimode filter
• LFO and input velocity can modulate any parameter
• 4x4 loop recorder
• Recording quantization and metronome
• Reverb, delay, chorus, flanger and phaser effects available on the send bus

The app requires headphones.
The app will be available for iPhone 4,4s and iPad 2,3 devices.

Estimated release date: July 2012

(Via the BeepStreet forum, with thanks to Matthias for emailing me the info)