An interesting puzzle concept is available in iEscape, iEscape LITE, and RabbitEscape (the last one is shown here to the right). They are all from the same developer, and basically just different packages around the same puzzle concept. The puzzles are closely related to Sokoban (see my earlier post on classic Sokoban ports for the iPhone). The difference to Sokoban is, in a nutshell, that the “blocks” to be pushed around are now placed in the edges of the graph, instead of on the vertices. So, one could call this “Sokoban on the edge”-puzzles.
Regular Sokoban is played on the nodes of a rectangular grid: you walk on a grid and push blocks around on this grid. The block completely fill a node and have to be pushed to another node if you want to pass. You can only push a block when there is a free space behind it. In iEscape (and its variants) the blocks are lines between the nodes of the grid. So instead of blocking the node itself, they block the transition from one node to another. In graph-theoretical terms, the block (line) is on the edge between two vertices. Like in Sokoban, you can only push a line when there is a free space (line) in the position into which you want to push the line.
This leads to nice little puzzles, although I have the feeling that the complexity can be raised substantially from the levels as available in RabbitEscape. The main game iEscape has a level editor built in, so this would allow for more complexity to the shared in the future. The current levels are just a proof of concept, but I hope for more of this in the future.
Further: please remove the stupid time restriction!!! You only have limited time for each level, and when you failed three times to finish the level before the time runs out, you have to start all over again (yes, completely all over, repeating all levels you already solved). At least let us puzzlers do this on our own pace, and add a playing-mode without clock, and with free level choice.
FInally, don’t try RabbitEscape. It says to have 21 levels, but actually the second ten levels are just reflections of the first ten levels. I felt a bit screwed when I realized this!
[Update 21 March] RabbitEscape has been updated, and now there are 21 different levels. Interestingly, some of the mirrored levels have only changed minimally—but the effect is that the solution is completely different. Unfortunately, the puzzle still has a very strong time-constraint. This makes it more a puzzle of memorizing the solutions than to find the solutions.