Users mark squares on a 16×16 grid. A mark's vertical position determines the note, and its horizontal the time. After 16 steps the sequence loops back to the start. Tunes can't be exported (though output is easy enough to record with something like Audacity), though compositions can be copied to the clipboard as strings of numbers, and pasted back into the application or shared. The ability to make by drawing (free hand, reproducing sprites, etc.) makes it a fun way to generate small melodies, stings, and probably etc.
It also works well as an improvisation instrument. With a line out to an amp, or using something to record output, longer songs can be improvised by modifying the patterns to be played in the current and the following loop. A text file with a list of prepared loops to paste into the application can also be a good tool. See ToneMatrix Improvisation 001 below for an example.