I found another one! This time it's a program.
It's called Open Song Composer. It's quite easy to use really, just click 'Make me some music!' and off you go! You will need Java for this, though. To open it, go to the folder where you had unzipped the Open Song Composer into, and open the folder called 'openComposer'.
Open the folder called 'dist'. You will find a .jar file called 'Open_Song_Composer'. Right click it, Open With, look for more programs. Open it with Java(TM) Platform SE Binary. It will take a few seconds, but when it finally opens, just click 'Make me some music!'. Now, save it in a folder of your choice with the name '<name here>.mid'. [I really recommend you save it as MID].
That's it. Just keep generating music!