pD POD !
"pdPod allows the creation of interactive musical applications for the iPod. It integrates Pure Data (http://crca.ucsd.edu/~msp/software.html ) a visual sound programming language by Miller Puckette which allows the rapid development of musical applications. Guenter Geiger (http://gige.xdv.org/ ) has made PDa (http://gige.xdv.org/pda/ ), a port of Pure Data for PDA Linux devices which we recently adapted to run under iPod Linux as well. Martin Kaltenbrunner (http://modin.yuri.at/ ) created a GUI application which allows the execution, display and control of PD patches on the iPod. This application was made by the creators of the reacTable at the Music Technology Group (http://mtg.upf.edu/) at the Universitat Pompeu Fabra in Barcelona, Spain.
This instrument was made possible thanks to the efforts of the iPodLinux (http://ipodlinux.org ) project, which provides a Linux environment for the iPod. pdPod itself can be downloaded from its WIKI page (http://ipodlinux.org/Pdpod )"
I'm sure I've posted on pD POD before, but this video was a good example of it running. iPodLinux runs well on 3rd Gen iPods and these are cheaper on eBay these days, so I may venture into pD Pod at some point.