Rocket.Chat - Rocket.Chat is a Web Chat Server, developed in JavaScript, using the Meteor fullstack framework.
Airtable - Airtable works like a spreadsheet but gives you the power of a database to organize anything. Sign up for free.
Slack - A messaging app for teams who see through the Earth!
Microsoft Teams - Microsoft Teams provides the enterprise-level security, compliance and management features you expect from Office 365, including broad support for compliance standards, and eDiscovery and legal hold for channels, chats, and files.
Dialog Messenger - handy and feature-rich enterprise multi-device messenger available for server or cloud – Slack-like, but not Slack-limited
RingCentral Video - Live life unlimited. Free video meetings and team messaging in one app that works the way you do.