A work in progress:
The yellow lines are live spectrum analysis of the playing music (Rhythmbox, line-in, mic, etc.).
You place boxes around, and the boxes are activated by the amount of activity below them (visualized by the white line).
The interface is one-click simple so it should work great on touch-screens.
This app joins a host of other Luz input methods— MIDI pianos and consoles, joysticks and gamepads, keyboards and mice, laptop touchpads (as absolute X/Y pads), wacom drawing tablets, and wiimotes.