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In both Gmail and Outlook.com, you can set up tasks, which are ToDo items that can have a due date. Tasks are accessible through a browser and there is a Windows 10 desktop or Android app for viewing them. Tasks created in Outlook.com will appear in desktop Outlook if you've included your Outlook.com email account.
Google tasks are created and managed through Gmail. Although you can set due dates for your tasks, there doesn't appear to be any way of coordinating your tasks with your calendar.
Apple iPhone synchronizes Outlook tasks with its Reminders app.
Between the two, I find the Outlook.com version to be better because it can include more detail in each task but I use desktop Outlook for managing tasks.