Slack - A messaging app for teams who see through the Earth!
LAN Messenger - LAN Messenger is a decentralized UDP IM-style chat client which supports usernames...
Skype - Stay in touch with your family and friends for free on Skype. Download Skype today to chat and call on desktop and mobile.
MyChat - Secure instant messenger for any network
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.
BORGChat - BORGChat is a LAN messaging software program.