Streampad, developed by Dan Kantor is a full-featured web based music application that runs inside a web browser, and give users access to their digital music library from any computer.

How it works:It's a free service, that requires "Java desktop application" to store the metadata from all MP3 and AC3 files (protected and unprotected), that it finds on your computer, including those that come from iTunes.

When, this user logs into Streampad from another computer, he /she can listen to the music directly streamed from their previous computer.

“The song is streamed from your own computer when you request it,� said Daniel Kantor, founder of Streampad. “When you run the Java program, it continues to run and act like a Web server so the request is going to your own system. Basically it works the same way a "peer-to-peer" system would work. As you’re choosing the music, all that info is coming from Streampad, my server, but when you play that music, it comes from your computer.�
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Streampad

Online Stream Your iTunes To Any Computer Using Web-based Media Player, Streampad