As others note, it's trivial with tinc to setup mesh networks, with both direct and indirect routing among peers. It's the basis of CCC's ChaosVPN.[0] Also, it works well as a Tor v3 onion service, and so provides an alternative to OnionCat, which will become unusable when the Tor Project deprecates the v2 onion protocol next year.

0) https://wiki.hamburg.ccc.de/ChaosVPN