Michael Gilbert has come up with a terrific puzzle app game called BoxOff. The object is to remove all the circles. See the first image - those are the rules. Essentially: connect a red circle to another circle to form a rectangle of any dimensions provided that there is no other circle - of any color - in that rectangle.
The second image is a sample puzzle of that.
See the third image? That version is called Stacks. The same rules apply except that the top circle will come off first.
There is a third version of this game! The objective is to remove all the circles under the rules, but now you must maximize the area of your rectangles.
Each version has 23 levels. I have not completed any of them. They get tough!
BoxOff easily makes its way onto the prestigious List of Best Puzzle Apps of 2014
Update 2/27/15: Michael Gilbert is the developer of BoxOff, but the game was invented by Steve Meyers. BoxOff was featured on the cover of Games Magazine last year.