I found one called Anvil Studio. It's free and not too facy, but basically it's like a big keyboard that records notes.
I made some mood music with an electric bass a minute ago so it's easy.
Really it's more of a .wav maker though since it only one note per spot. So like you can't mix in high, and lows at the same time. Makes great Terminator style music though. boom boom boom baaaaa boom boom boom baaa lol
Do a search and you should find it. If not I'll try to post a link later but I'll have to go re-find it.
He who stands on toilet is high on pot!