I'm not releasing the code publicly yet but I've written a tool that lets ANY user of this instance direct message EVERY OTHER user of this instance through a proxy account (so people can block the proxy if they want).
Why would we want this? Friend Camp is a small (70 person, 40 active) invite-only instance of people who trust each other. We like to organize events (book clubs, etc) but not everyone sees everything. So this is for doing that kind of thing.