Frank's Java LED Synthesizer 2.6 is a program that let's you compose music. it lets you create a pattern that loop.
the pattern is a table of cells. when a cell is on, it plays a note.

I got the idea for this program from the Bliptronic 5000 LED Synthesizer

you can download the program here
you can download the source code here

you can download a old version in the archive

you can read the tutorial here

you can download the example songs here
tip: you can open the song zip archive directly, just go to file->open and select it

here are the keys for this program
-: decrease volume
+: increase volume
[: zoom out
]: zoom in
q: decrease length of pattern
w: increase length of pattern
a: transpose pattern up
z: transpose pattern down
s: shift pattern left
d: shift pattern right
x: choose left notes
c: choose center notes
v: choose right notes
f: repeat the pattern or song
space: play or pause the song