Zulip - Chat for distributed teams. Zulip combines the immediacy of real-time chat with an email threading model. With Zulip, you can catch up on important conversations while ignoring irrelevant ones.
Flow - Stop managing projects from your inbox.
Slack - A messaging app for teams who see through the Earth!
Rocket.Chat - Rocket.Chat is a Web Chat Server, developed in JavaScript, using the Meteor fullstack framework.
Rendevu - Rendevu centralizes the different tools your team uses (GSuite, Slack, Trello) and streamlines your workflow.
Noor - Chat like you're in the office together