LAN Messenger - LAN Messenger is a decentralized UDP IM-style chat client which supports usernames...
Dialog Messenger - handy and feature-rich enterprise multi-device messenger available for server or cloud – Slack-like, but not Slack-limited
Feem - Share files offline. No servers. No cloud. No limits.
Ripcord - A desktop chat client for Discord and Slack
BeeBEEP - You can message and share files inside your intranet without a server.
Done Hui - No need to switch between multiple pieces of software to get through the workday. CHATS: Communicate freely. CALENDAR: Know your team's availability, plan meetings. No more conflicts. TO-DOs: Stay on top of all projects. FILES: All files, one spot.