The Invisible Internet Project (I2P) is a garlic routing using overlay network and darknet that allows applications to send messages to each other pseudonymously and securely. Uses include anonymous Web surfing, chatting, blogging and file transfers. The software that implements this layer is called an I2P router and a computer running I2P is called an I2P node.
License: Open Source
OnionCat is a lightweight and simpler solution for achieving anonymity in various applications, while I2P offers a more robust and decentralized network with strong privacy features but requires a more complex setup.