Secure instant messaging system for team collaboration
LAN Messenger - LAN Messenger is a decentralized UDP IM-style chat client which supports usernames...
Thunderbird - Thunderbird is a free email application that's easy to set up and customize - and it's loaded with great features!
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.
Microsoft Outlook - Organize your world. Outlook’s email and calendar tools help you communicate, stay on top of what matters, and get things done.
Bopup IM Suite - Organize secure messaging system and communicate instantly via self-hosted IM server.
eM Client - eM Client is a fully-featured email client for Windows and macOS with a clean and easy-to-use interface. eM Client also offers features for calendars, tasks, contacts, notes, and chat.