Kim Duckworth recently contacted me about his new puzzle app game Cogismo.
  The object is to get each number to Zero. Tap on any circle and it will rotate clockwise and increase by 1. Cogs will collide with neighbors and those neighbors will also go clockwise.

Cogismo is a great concept. It's tough!  Very tough. 
In my opinion, there should be a very easy gird to start with, say 1x3, then 2x2, then 3x2 and finally 3x3.

It's free!  So give it a test and feel free to add your comments below.
https://cogismo.com/
https://itunes.apple.com/app/id1125257501
https://play.google.com/store/apps/details"id=theguild.cogismo.std

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