There is also a graphical user interface for PPL called ppli . In Unix, it can be accessed by typing wish ppli at the command line. The complete source distribution as a gzipped tar file. The complete source distribution as individually downloadable files. To run ppl, you can either download one of the pre-compiled binaries, or a bytecode version which needs the Objective Caml runtime system.
All software mentioned above is available free of charge.
Versions are available for all major platforms. See the GNU General Public License for more details.