game-editor.com

I found this amazing app. If you have an iPhone or iPod touch, get it, it's completely worth the twenty bucks.
Built-in keyboard, sequencer, 21 professionally sampled instruments, customizable effects... it really puts the power in your pocket.
Here's the trailer for it.
And click here to listen to a piece I made with it.

Another piece: http://www.youtube.com/watch?v=HfZfpmq1-rs

I would like to compose midi with anvil studio in linux...

Cool. And you can save the music onto your computer?