Here’s a cool puzzle game by Nicky Case.
It even works pretty well on mobile devices.

“Mind-bending, Space-rending, and Completely Innocent Creature’s Life-ending.

In this negative-space puzzle game, you’ll drag around holes, fall through walls, and bring myriads of miniature Monsters to madness.

Say you sadistically hunger for more levels, or you just detest the levels I’ve made. That’s fine, you can play negative-space puzzles created by other Newgroundians! And you too, can make your own.

Use the Level Creator to design your very own puzzles, and share them with a cold uncaring world. More Monsters to torture, for the good of everyone else!

Think outside the box, fellow monsters.”