Back when I used to keep all of my music on my Linux box, and iTunes had recently become available, I wanted to be able to stream that music as though it were being hosted by iTunes on a Mac. To that end I wrote iCast. It has some significant short-comings as I recall, but it does work. Or at least it did, five+ years ago when I wrote it. I don't know to what extent DAAP has changed since then.
It's got some cool code for traversing a music collection, parsing ID3 tags and determining song length and average bit rate by using my own MPEG audio frame parser. Yeah, this was more a labor of love than a practical approach at creating an iTunes music server. That's par for the course.