[Mainsail]

I may be making this up, but I seem to recall a chat feature on one of Napster, Limewire, or Kazaa.

[ghotli]

Soulseek is likely the one you're remembering. I remember talking to people with similar collections of music. Hotline was my primary passion for quite some time but soulseek had a longer run of utility in my childhood on the nascent web.