OnionCat creates a transparent IPv6 layer on top of Tor's hidden
services or I2P's tunnels. It transmits any kind of IP-based data
transparently through the Tor/I2P network on a location hidden basis.
You can think of it as a peer-to-peer VPN between hidden services.

Having Tor/I2P installed is not required for building.
The Tor/I2P installation does not have to be from SBo.