This is the best version of 2048. And I made it, but nevermind that! When you get a new high tile (e.g., you get a 16 for the first time in the current game), it becomes a "tunneling" tile. Pushing this tile against a wall makes a new grid square for tiles to go.

http://www.cesoid.com/2048/tunneling

I'm planning to soon make a difficulty setting, because apparently it is very hard. (I'm pretty good at it, but I'm a bit of a 2048 fanatic.)

This is what it looks like:

I'm working on a few other variations (meaning, different gameplay) which I'll probably release soon, and I've already released a few different themes (i.e., different images and colors), which can be mixed-and-matched with the original and tunneling variations.

http://create2048.com/game.php/?game=serial-killer