I2P is an alternative anonymity network to Tor which supports most common Internet activities like web browsing, email, filesharing etc. Unlike Tor, whose main focus arguably is on accessing sites from the "normal" Internet, I2P is more oriented towards being a closed darknet, separate from the "normal" Internet. Any one running I2P can run an anonymous server, a so called Eepsite, that is only accessible within I2P using the .i2p top level domain (similar to .onion for Tor hidden services). For instance, the I2P homepage can also be accessed through I2P via http://i2p-projekt.i2p.

I2P is not started by default in Tails, but can be started manually throught the menu:

Applications -> Internet -> I2P

Once started, the so called router console will open in Tor Browser, which shows I2P's current status, links to many useful I2P resources (forums, email, filesharing etc.) and offers the possibility to shutdown I2P. I2P is integrated in the browser in such a way that all .i2p addresses are accessed correctly through I2P while all other addresses are handled by Tor, all at the same time.