Yggdrasil and GNUnet seem like more interesting alternatives to me (with cjdns and hyperboria as cousins). Although these do not build on wireguard, they employ the same basic stack (plus some to handle a mesh topology).

Is that like Hamachi? https://vpn.net/

What is the difference between this and ZeroTier? https://www.zerotier.com/

Works only with some identity providers, for some reason I could not understand. If you don’t have a Google, Microsoft or corporate email identity provider, you can’t use it.

There might be a reason for this, but still it’s not in the same space as Wireguard.