Pd is a real-time graphical programming environment for audio and graphical
processing.  It resembles the Max/MSP system but is much simpler and more
portable; also Pd has two features not (yet) showing up in Max/MSP: first,
via Mark Dank's GEM package, Pd can be used for simultaneous computer
animation and computer audio.  Second, an experimental facility is provided
for defining and accessing data structures.

WWW: http://www-crca.ucsd.edu/~msp/software.html
Unofficial WWW: http://puredata.org/
