Just finished my latest app. It's called Wavematrix, and can be found here. It's inspired by Tonematrix, a Flash application somebody made. I just extended upon its functionality, and made it a bit more fun. It allows you to create sound or music in just a few minutes.
You should try it out and leave me some feedback. So far, release 2 and release 3 (coming soon) sound much better than release 1, which was there first (hence the bad rating). I was experimenting with sine-waves in that release, and it didn't turn out so well. I suggest you give the latest release a try.
I have attached a screenshot. You basically use your finger or mouse to "paint" some music. Due to the 16X16 dimension matrix, almost every pattern will end up sounding well. By clicking the "plus" button, you can add more matrices next to the current one, to extend the tracks length.