a service that is out in the market already for some considrable time; with more than 4m users; a service with which sheet music can be bought, and sold. maybe musicians know this service; maybe not. i for one, never heard about it... but then again, I'm not a musician at all :) i think the marketplace is nicely designed with easy to understand user interface, easy to use search function, enormous library and previews of the sheet music with snippets of audio. nice hunt!