LAN Messenger - LAN Messenger is a decentralized UDP IM-style chat client which supports usernames...
Slack - A messaging app for teams who see through the Earth!
Softros LAN messenger - LAN messenger for an internal office chat for home or business users. It does not require a server and is very easy to install and use. It supports personal chats, group chats, message brodcasting, files transfer and remote desktop access.
Telegram - Telegram is a messaging app with a focus on speed and security. It’s superfast, simple and free.
MyChat - Secure instant messenger for any network
Mattermost - Mattermost is an open source alternative to Slack.