Fantastical 2 - Fantastical, the Mac calendar app you'll enjoy using. Quickly create new events with natural language input and more.
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.
Microsoft Outlook - Organize your world. Outlook’s email and calendar tools help you communicate, stay on top of what matters, and get things done.
Todo.txt - Track your tasks and projects in a plain text file, todo.txt. A todo.
Morgen.so - All-in-one Calendar, Tasks & Scheduler. Morgen is the single hub for everything that revolves around time management.
Task Coach - Task Coach is a simple open source todo manager to keep track of personal tasks and todo lists.