I've been following this thing update by update since first betas few years back. The "Firefox" of media players. It is, of course, Songbird: iTunes Killer
Like Firefox and iTunes mashed together and the entire thing is customisable top to bottom. Loads of great little addons like one that can get you the lyrics of almost any song you play... handy!
I don't use it often myself because I haven't worked out how to sort out my bookmarks and feeds on it, and if I recall its a bit bloaty to use. However, its a work continuously in evolution, gaining features with to-do lists of things that aren't even possible yet.
Of course, its main tag was that you could "play the net". At the time mp3 blogs were a relatively new phenomenon so I didn't quite cop what that meant. You can just dive onto Hype Machine and whatnot and it'll automatically make a little web playlist at the bottom of the page of the files on offer and easy drag and drop if you want to store and keep the mp3s. /videos of course.
I've seen it! Its the future!