Thunderbird - Thunderbird is a free email application that's easy to set up and customize - and it's loaded with great features!

Microsoft Office Access - Access is now much more than a way to create desktop databases. It’s an easy-to-use tool for quickly creating browser-based database applications.

Microsoft Outlook - Organize your world. Outlook’s email and calendar tools help you communicate, stay on top of what matters, and get things done.

LiveCode Platform - It is Both Under the GPL and it is also Proprietary if using the GPL version the software you make...

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.

MongoDB - MongoDB (from "humongous") is a scalable, high-performance NoSQL database.