Empathy - Apps/Empathy - GNOME Wiki!
Thunderbird - Thunderbird is a free email application that's easy to set up and customize - and it's loaded with great features!
Gajim - Full featured and easy to use Jabber client
Microsoft Outlook - Organize your world. Outlook’s email and calendar tools help you communicate, stay on top of what matters, and get things done.
IM+ - Chat everywhere! IM+ is the most widely used mobile IM app! Connect all-in-one to MSN, Yahoo!, Goo...
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.