Saw a neat tweet from Dave Radcliffe this afternoon:
My younger son had a half day of school today and I was looking for a short project to do with him – this game fit the bill perfectly!
Basically I launched the game and turned on the camera. Here’s what a kid seeing the game for the first time thinks:
Although he struggled to make the first set of shapes, you can see right away that the game gets kids thinking about factoring in a non-standard way. Having figured out at the end of the last video that a correct solution will fill the whole square, we made a second attempt. There’s lots of great problems to solve in this game:
Next we tried to go to another level of the game, though we didn’t initially know how to do that! Eventually we did find some more levels and gave one a try, and the ideas he learned from solving the first puzzle helped him get through the second level much faster. At the end he even wanted to try to make his own level!
So, a really great game for kids. Nice little puzzles to solve, and also a sneaky way to get kids thinking about factoring. Fun little project!
Mike's Math Page 
It is a very idea: integral use of the array/area model for multiplication and nice that you can create your own puzzles. It would really benefit from some structure/curation around the user created levels, though. Some (many?) are just drafts, not many are carefully thought out, and there is no sense of progression from easier to harder.
Note that the list only shows the last 50 created. If you want to explore others, the URL structure is:
http://bojagi-gotmath.rhcloud.com/show/%5Bn%5D
replace [n] by the number you want to see, like:
http://bojagi-gotmath.rhcloud.com/show/143
Maybe other interesting questions for your sons are whether there are any constraints the numbers have to satisfy to have a solution? Also, is it possible to have a bojagi with multiple solutions?