Zerotier is typically used for privace networks, and AFAIK it routes through a central server whenever p2p is not possible. On the other hand, the Yggdrasil mai

Zerotier is typically used for privace networks, and AFAIK it routes through a central server whenever p2p is not possible. On the other hand, the Yggdrasil main net is a public network, and each peer is a router. You don't (and can't practically) connect to every single peer, but any nodes in the middle can route things the right direction. Also, Yggdrasil can run on top of existing tcp/ip like zerotier, but it can also run on custom mesh base protocols.