PolyPitch is released under GNU GPL 3, for SuperCollider 3, by Nick Collins 

To install: put the PolyPitch folder in your SC extensions directory. Copy into that folder a PolyPitch.scx file. There are some prebuilt ones provided for OS X, and compilation instructions also follow. 

Prebuilt versions for OS X are in the prebuiltversions folder.  

To compile for platforms other than Mac, using the SC native FFT interface, comment out:
#define OSXACCELERATENOTSCFFT
in MultipitchHeader.h

Compilation requires libsamplerate from http://www.mega-nerd.com/SRC/

Compilation example: 64 bit (e.g. SC 3.6)
Make sure in CMakeLists.txt that the 64bit library linking line is uncommented and 32bit is commented
Then on the command line (assuming CMake is installed and you have the source code of SuperCollider at /data/gitprojects/scdev/supercollider):
cmake -DSC_PATH=/data/gitprojects/scdev/supercollider -DCMAKE_OSX_ARCHITECTURES='x86_64'
make

Compilation example: 
32 bit on OS X

Make sure in CMakeLists.txt that the 32bit library linking line is uncommented and 64bit is commented

Then on the command line (assuming CMake is installed and you have the source code of SuperCollider at /data/gitprojects/supercollider):
cd into build directory
cmake -DSC_PATH=/data/gitprojects/supercollider -DCMAKE_OSX_ARCHITECTURES='i386' ..
make
 
