A month or so back a few Larpers at a conference called gather started talking about how Slack had sort of taken over communications in IT
(slack.com) . Then, we started talking about how we could maybe use it for Larp. You can set up dedicated channels, direct message people, and set up private channels, as well as the usual general public chat channels.
I went and set one up because it was worth a shot. There’s a form here that should auto-invite you if you give it an email address:
Sign-up and give it a shot.