Xmove15 is a small, but fun puzzle game that involves moving numbers around a 4x4 board until you get them in the order 1 to 15 (with the numbers wrapping from the right edge to the left edge on the next row). You control a cursor that you use to move the numbers: put the cursor over a number next to the empty spot, and the number and the empty spot will be swapped when you press 2nd.
Just like with XprO's other quality game, Xsnake, Xmove15 features great TI-Basic code. The game makes ample use of control structures, with a very easy to follow organization and setup, as well as showcasing several optimizations for speed and size. Simply put, it is a lot of fun to look at the underlying code, and to see what is possible in a small number of bytes.