EssentialPIM - EssentialPIM is a free Personal Information Manager that keeps up with the times and lets you manage appointments, tasks, notes, contacts, password entries and email messages across multiple devices and cloud applications.

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

Todo.txt - Track your tasks and projects in a plain text file, todo.txt. A todo.

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

Task Coach - Task Coach is a simple open source todo manager to keep track of personal tasks and todo lists.

Mailbird - Mailbird is the best email client for Windows 7, 8 and 10