IMC2
IMC2 is short for InterMud Communications Protocol Version 2. Similar to I3, IMC2 connects MUDs using TCP connections and allows MUDs to connect without server administrator permission. The IMC2 protocol supports multiple routers on a single network in a way similar to I3 (and did so a lot earlier). However, one of the ways that IMC2 differs significantly from I3 is that it does not use so called mudmode connections, making it much easier to implement IMC2 on muds not written in LPC.
Currently, there is only one active IMC2 network in use, MudBytes InterMud Communication Network.
Read more about this topic: Inter MUD