Spotify was originally p2p. The early principal engineer was the same dev who built µTorrent, Ludvig Strigeus.

I'd also recommend looking at communities such as Soulseek. And Limewire is still around!

Thanks for the info although I was around during the released of µTorrent and one of its early users, I didn't know Ludvig Strigeus was instrumental in the Spotify early days.

Apparently he also the original author of OpenTDD and ScummVM, and it seems that he's the legit Carmack 2.0 [1].

[1] Ludvig Strigeus:

https://en.wikipedia.org/wiki/Ludvig_Strigeus