Designed by Ferdinand Lammertink, copyright ThinkFun 2005.
(plastic, 3 inches by 6.25 inches with 1.5 inch diameter wheels)

Two tracks, each with five squares, can slide horizontally to three positions (left, center, and right). Each square has the same number on both sides, A pair of wheels on either side of the central 2 by 3 array of numbers can be used to flip them. The basic goal is to make the pattern 0 to 9 (i.e., 0 to 4 on the top row and 5 to nine on the bottom row). The directions also challenge you to make other patterns.

Further Reading
Jaap's Page, from: http://www.jaapsch.net/puzzles/flipside.htm
Passion For Puzzles Page, from: http://www.passionforpuzzles.com/puzzles/flipside.php