#Reticulum has this concept built into the networking stack. Trusted and closed networks can interoperate with open and untrusted networks. Authentication is built-in. This allows for networks that form and dissolve easily without having to trust the underlying infrastructure.

https://reticulum.network/manual/networks.html
LXMF is a transport protocol similar to Nostr that is built with the Reticulum networking stack.

A comparison of Nostr and Reticulum

https://github.com/markqvist/Reticulum/discussions/59

Summary:

"In some ways, it [Nostr] is very similar to LXMF, in that it also has the "dead-drop" and wide distribution mechanism. It is different that LXMF offers forward secrecy and encryption by default, while still allowing the posting of public or semi-public information."