So it would work by having a "server" calculator, and anyone could add their account to the "server" calculator, send messages to it for other people to see, and received any messages people have sent since the last time you received messages. Each server would have a username and password system to prevent impersonation.

I recall one instance of online calculator gaming being possible with Obliterate for monochrome Z80 calculators over the Global CalcNet bridge, but I don't know if it's still online. I remember some IRC client as well but I forgot the name.

I'm sure this project is partially pissible on monochrome 84+ calculators if you have enough Z80 programming experience but if gCn is still online the I'd recommend trying the IRC client in the Cemetech downloads section instead to see if it already does most of what you need (impersonation will be possible, though).