Hallo!
matlab code can be easily ported to python+numpy or ruby+narray. the amplitude stuff and tagging are the easy part once you've managed the tempo detection.
if you want to be opensource you could also use octave - which is something like a free matlab clone ... There is also a GUI project for octave, then you could do something like you want to ... but I don't know if this project is already ready to use ...
LG Georg