Google Calendar is a powerful and flexible calendar app that's free to use with a Google account. It integrates nicely with other calendar services and offers features like sharing, customizing views, and integrations with other apps through Zapier. Microsoft Outlook Calendar is another top option for teams and individuals alike, offering a range of enterprise features and seamless integration with Microsoft Office apps. For scheduling external appointments, Calendar is a great choice due to its modern design and easy-to-use interface. Apple Calendar is a simple yet powerful app that integrates seamlessly with the rest of the Apple ecosystem, while Fantastical offers a premium design experience with natural-language event creation and advanced features like Focus Mode-based filtering. Ultimately, the best calendar app for you will depend on your individual needs and preferences.