– Tor
I think this is the most popular p2p network today.
Tor is free software and an open network that helps you defend against traffic analysis, a form of network surveillance that threatens personal freedom and privacy, confidential business activities and relationships, and state security.
Tor can be used to run hidden services with .onion domain.
Site: www.torproject.org
– Freenet (File sharing)
Freenet is a peer-to-peer platform for censorship-resistant communication and publishing. It has no direct routing, sites are stored as files with routing key.
Site: freenetproject.org
– I2P
I2P is an anonymous overlay network like Tor. It is intended to protect communication from dragnet surveillance and monitoring by third parties such as ISPs.
I2P can be used to run hidden services with .i2p domain.
– ZeroNet
Much like Freenet, but uses bitcoin cryptography. Sites are served by visitors.
Has .bit top-level domain.
Site: zeronet.io
– Freifunk/ChaosVPN/DN42
This is a group of VPNs and mesh networks.
Main IP ranges: 10.4.0.0/16, 10.32.0.0/16, 10.100.0.0/14, 10.104.0.0/14, 172.31.0.0/16
– Alienet
Alienet is a vpn based hidden network, close (you can’t use it like a proxy, nor any proxy will be able to enter it). It bears around concepts related to anonymity, privacy and security.
In Alienet you’ll be able to visit the ‘.anon’ sites: it looks like a parallel network, out of all, indipendent, uncensored and among all secure.
– Neptilla
Neptilla is small p2p network designed by the group of mind-like individuals to exchange and store knowledge. Now seems to be down.
Beyond that, there are many smaller p2p networks which are not listed anywhere and requires an invite.