Let’s Chat is like #Slack, but opensource and self-hosted. It is a persistent messaging application that runs on Node.js and MongoDB. It’s designed to be easily deployable and fits well with small, intimate teams. It’s free (MIT licensed) and ships with killer features such as LDAP/Kerberos authentication, a REST-like API and XMPP support.
Read more: https://sdelements.github.io/lets-chat/