Corptabs - Corptabs is a secure and reliable cloud-based communication software that allows organizations to connect businesses and employees with dynamic broadcast messaging.
Thunderbird - Thunderbird is a free email application that's easy to set up and customize - and it's loaded with great features!
CallzApp - CallzApp, world’s only dialer app that can prioritize communications
Microsoft Outlook - Organize your world. Outlook’s email and calendar tools help you communicate, stay on top of what matters, and get things done.
Drupe - Next generation contact manager and dialer.
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.