Napster 2.0 was originally called Duet, then renamed to Pressplay. This was created by the original MP3.com and not the corporate bastard child taking the current name of MP3.com. Roxio had bought the name Napster, then came to MP3.com to use pressplay for the back end. They then ripped it out of the MP3.com group of products and struck out on their own, renaming pressplay to Napster 2.0. The back end was well designed last I saw of it, but I can't vouch for what has been done with it since they moved off on their own.
For the LAMP lovers, it did run on Redhat 6.2-9.0, with apache 1.x, MySQL 3.23.x and tons of 'drunken coded' perl and a few other fun languages. No telling what it is now, but you might still see mention of duet and pressplay in urls and in random guts of the programs.