Came here to say this. Mattermost runs really well on a small-ish box, self-contained, has never gone down, and we've been able to grow organically to hundreds

Came here to say this. Mattermost runs really well on a small-ish box, self-contained, has never gone down, and we've been able to grow organically to hundreds of unique users a day all inside the firewall. Pretty much a no-brainer for me.