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
Strikethru - Strikethru is a kind of to-do list notebook for managing work lists and staying updated with the important tasks.
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.