comes from Peng Wan. It's a gem. The object is to move the yellow square in the bottom grid to control the blue square in the grid above and get to its destination.
More advanced levels include a sokoban element with wormhole for either the yellow or blue squares.
What's particularly interesting is that sometimes the grid below is smaller than the one above. It leads to some very interesting puzzles.
There are some 400 levels. At the moment I've done about 120.