Invisible Internet Project (I2P) (opens in new tab)

The issue I have with i2p is that it enforces all clients to be exit nodes, too. It makes the peer system stronger, but also legally vulnerable.

[update: this isn't true anymore, there's a config flag now available that fixes this and outproxy=false is defaulted. See [1]]

[1] https://geti2p.net/en/faq#exit

Protocol-wise they're pretty similar except I2P uses a variant of onion routing called "garlic routing" which allows for message bundling (I don't know if this is currently used beyond bundling for delivery status messages and lease sets). I2P also has unidirectional circuits as opposed to Tor's bidirectional ones which means unlike Tor hidden services where you build a bridged circuit using a rendezvous point, in I2p each side has a pair of unidirectional tunnels for send/receive. I2P is also packet switched as opposed to circuit-switched, which can possibly make it more resilient to traffic-analysis attacks and lead to better load balancing of resources.

Otherwise the main differences seem to be design-wise, where in Tor you rely on a centralized bootstrap to get the list of relays whereas I2P does this via decentralized NetDb.

Roughly it's like Tor (though I think the transport is not necessarily like Tor), except it's closed. You can only communicate with others on the I2P network. Some I2P users may choose to operate an "outproxy" and provide Internet access but it's not built into the network or software. What is (or was, it's been awhile) built in is a torrent client.

It's also written in Java and the router web UI was pretty snazzy from what I remember.

Unlike Tor, I2P supports UDP which lets you use bittorrent, but since I2P doesn't have exit nodes, you can only bittorrent with others on I2P.

Zerotier is great for this.

There's a few I2Psites that track other I2Psites (and share hosts.txt files). You can subscribe to these (attaching *.i2p domains to their respective long base32 links). By default stats.i2p and a few others are in your address book.

There used to be some I2P-only search engines but I'm not sure if they exist anymore.

I2P is basically just an anonymous network layer. It doesn't store files, proxy to the internet, run a web server, etc. All it does is anonymously connect standard servers and clients.

Freenet on the other hand is an anonymous content distribution system. You can't use it to connect arbitrary network services together, it's only good for storing and retrieving files. Nodes on Freenet each store encrypted pieces of data but it's computationally hard to figure out what data a particular node is storing unless you have the key to access it. Files are prioritized based on popularity so old files that no one has accessed in a while and the original host is gone can just be lost forever. It's similar in some ways to bittorrent swarms. Over time as a torrent becomes less and less popular you're likely to run into issues finding a seeder that's still around.