Fantastick is free

Fantastick is currently free, no idea for how long though, and has also been updated so that it is a universal app now.

Use your iPhone/iPod/iPad with Max/MSP or Pure Data!

Fantastick turns your device to a custom multitouch controller. Send multitouch data to the host program and receive drawing commands.

Instead of a limited set of builtin-widgets, the interface logic resides in Max/MSP and only drawing commands are sent to the device. Build interfaces that ..

• work and look exactly the way you want
• change dynamically to fit the musical context
• are experimental and would not be possible with other apps

Watch this intro:
http://www.youtube.com/watch?v=WWYF9pB2nzc

Features

• Minimalistic, fullscreen control area with nothing on it but what you provide.
• Multitouch-events on the device are forwarded to your host via UDP. Information includes the touch state (begin, move, end) and coordinates for all touch points.
• Designed for no-hassle: zero-click startup, the device does not sleep or suspend network connection, flicker- and lag-free.
• Displaying images (fetched with URLs) and caching them on the device for use on non-networked locations.
• Basic drawing with lines, boxes and text.
• Advanced drawing with OpenGL.

Visit http://pinktwins.com/fantastick for quick start and usage examples.

NOTE: this app works together with other software. When launched you get a black screen, what happens then is up to you. Visit the website for examples and documentation.