Tinc, a GPLv2 mesh routing VPN
Tinc is incredible, it has worked flawlessly for me for 6+ years with exactly 0 maintenance.As trustworthy as it is, I am sadly on the hunt to replace it.  Compared to wireguard, the throughput ain't great, and it takes way too much CPU on my low power nodes. I would pay good money for "tinc, but with wireguard transport" -- there's of course projects purporting to do this but I haven't found one I trust yet.