Chain3 is an upcoming puzzle game for the iPhone from Indie developer Shawn McGrath. It functions in the common match-3 framework, but it allows for any piece to be dragged anywhere with no restrictions. This means making a match is trivial, so the game is based on the idea of chaining matches so that one match causes another, and that causes another, etc.
After you make a match, the tiles will flash for a short time, giving you a chance to setup the pieces for the next match in the chain. Also, just before the tiles drop, there’s a brief pause, allowing you to slip pieces under falling pieces to cause chains, à la Tetris Attack.
There’s a YouTube video about Chain3, game information, and a detailed description of the game system.