TapTalk.io - TapTalk.io is a complete in-app chat SDK and messaging API - Easy integration and customizeable.
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.
Lets Chat - Open source self-hosted chat app for small teams
Airtable - Airtable works like a spreadsheet but gives you the power of a database to organize anything. Sign up for free.
MongooseIM platform - The massively-scalable XMPPJabber mobile messaging platform, for mobile and web, by Erlang Solutions
Creativity 365 - Cross-device content creation suite