ButtonBeats is a unique and great way to mess about with musical instruments online. The best thing is that is totally free and it sounds great.
“ButtonBeats.com was launched in august of 2007 by me, Jason. I had a set of music samples I wanted to mix up and I didn’t have any software available so I made a program to mix them up. My friend came over and was playing the program for over an hour. So I thought It would be cool to upload it to the internet. So I bought the ButtonBeats.com domain name and uploaded a few different programs I made. A short time later I made the piano. After about a year I got my friend Everett involved in producing the site and getting the name out there. From there we had a friend Ariel that made music. Ariel, Everett and I spent many afternoons recording sound samples,editing the samples, designing ui, making beats, ordering beats, designing t shirts, stickers, programming and barbecuing. Within the last year we brought Stephan on board. He has skinned the whole site with a new look this summer and has other good ideas in the works right now.” – the ButtonBeats Website
Why not try it out here