I run an annual challenge
http://www.pipool.org
and this year I wrote a Scratch simulator for people to play with
https://scratch.mit.edu/projects/161889306/
and I've started porting it to GP :)
https://www.dropbox.com/s/j9uixbjbjll72kb/pool.gpp?dl=0
PiPool Simulator
Moderator: MSandro