reference models

Several tools provide useful visualization for system dynamics. Unfortunately they are not easy to set up, and require mathematical and logical skills.

EVERYSYSTEM should be

POWERFUL as:
http://www.vensim.com/

but
EASY, INTERACTIVE and NON-RESTRICTIVE as:
http://www.algodoo.com/wiki/Phun
http://fold.it/portal/
http://sodaplay.com/
http://numptyphysics.garage.maemo.org/

REVEALING as:
http://www.bitstorm.org/gameoflife/

WITHOUT FORMULAS as:
http://vimeo.com/23839605

GRAPHICAL INPUT-OUTPUT as:
http://www.blender.org/development/release-logs/blender-242/blender-composite-nodes/