Idea by Jim Propp (with input from James Tanton), code by Valerie Samn. Please do not distribute this link without permission from Jim Propp.

Goal: Arrange the tiles in order from left to right in as few moves as possible
(in numerical order, or forming a word). Legal operations are
EXPLODE (select 2 tiles from same column; 1st goes left, 2nd goes right)
and UNEXPLODE (select 2 tiles that are 2 columns apart; both go to middle).
Click "New Game" to play, "Restart" to restart game, "Undo" to undo moves.
To cancel a selection, tap the tile again.