In my recent quest to build agent-as-primary-user tools I've built grpvn (https://github.com/frane/grpvn), a small Go/SQLite application that lets skill- and mcp-capable agents talk to each other. Biggest issue is the lack of a hook system so the agents can autonomously read and respond. Waiting for this to be supported, as IMO multi-agent teams talking to each other are an interesting next step.