Messaging platform I can self-host for my agents to communicate

I'd suggest MCP agent mail https://github.com/Dicklesworthstone/mcp_agent_mail I haven't tried it on a raspberry pi at all, but I have used it on my PC and Mac and it enables agents to message each other. It's a lot of fun to drop in on their conversations and observe how they address each other and co-operate!

Is this in the same office or the same LAN? If so, you could check out BeeBEEP.https://www.beebeep.net/ I think it shares more in common with ICQ than Slack, though.

I guess I should ask if by agents you mean people, or AI too.

Did you ask them if they wanted to talk to each other? I'd like to see the user research in this.