[plamzi]

There's also MSDP, MSSP, MCP. Google "mud protocol" and you will be well on your way.

ATCP2 is also known as GMCP. I prefer to use GMCP because it's basically JSON, not so much a protocol but a data-interchange format you can use to transmit any data you need to the client. The fact that it's JSON makes it very easy to parse in modern clients.

Quite a few custom clients have cropped up over the years, but the vast majority of MUDs don't even implement proper TELNET, let alone MUD protocols, let alone custom clients. KaVir's protocol snippet has made it easy for most Dikurivatives to add basic protocol support, but beyond that creating a UI requires a specialized set of skills.

A few months ago, I started , a site providing a cloud-based web app and a flexible framework for building custom MUD clients. Hopefully, as the bar gets lower and lower, we'll see more custom clients for more games.