Slack - A messaging app for teams who see through the Earth!
Element.io - Secure messaging app with strong end-to-end encryption, advanced group chat privacy settings, secure video calls for teams, encrypted communication using Matrix open network. Riot.im is now Element.
Skype - Stay in touch with your family and friends for free on Skype. Download Skype today to chat and call on desktop and mobile.
Chatib - Chatib is an online chat room where you can meet and chat with new people, make them friends, or even data them online.
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.
Kandan - Open Source private chat server. Your own private Chat server in minutes, plus additional features.