I used to use Cakewalk. It was great, because I could enter notes on a bar, and it would make the sound of the note when I clicked to insert the note. I could play back bits of it or the whole thing. Then Cakewalk got "upgraded" to the point where it seemed to be only for recording music and not sequencing MIDIs. Perhaps there's a simple solution, but I haven't found it.
I'll look closer at the programs Bill, but on first glance, they don't seem to be about writing music that I can play as a MIDI.