Soulseek

After two years this comment is still here - and we never got to know why one should avoid it "at all costs". Sounds really... naive? Let's look at some facts. Soulseek is an old, straightforward network, which runs fully on donation system. It doesn't contain any advertisement and functions which could implicate the gathering of user data - you don't need even an e-mail to register, so if you're effectively masking your IP (what you should do ALWAYS when using this kind of networks) - there's nothing to fear. Also because this network is not on any radar. Mostly you find there an old/alternative music gems for freaks, not the newest Marvel movies. The server is used for group messaging and search queries - everything is P2P there. And you have many open-source client for this.

Last thing, important. Not everything what's "propertiary" it's hundred percent bad. There's a lot of "open-source" products with much more aggressive financial model than Soulseek, oh boy! This network is simple, works stable from 20 years (!) and actually is community-driven from the beginning. Show me 20yo network which is open-source. It's really only up to YOU how you will use this network. Please - don't make a religion from open-source, because it not equals security. Don't make a "fancy fashion" from it, learn and be smart.

1. There should be "(...) everything ELSE is P2P there"
2. Sorry, I just need to add this: What you REALLY should avoid at all costs is Spotify, AppleMusic, Deezer, Disney, HBO, Netflix, your mobile ISP and local ISP. While avoiding your internet provider is rather a tough task - all of the rest, these are really pirate, unfair and aggressive companies - stealing from artist, building a system of exploitation. And you know what? I don't think that they will be still up after 20 years... ;)