Google Maps for Android has had the ability to give you reminders of when you need to leave for your next appointment. It is a handy feature and it takes into consideration things like traffic conditions to make sure you leave in enough time to make that appointment. Now that same feature has rolled out to the web version of Google Maps.
With a change of the notification settings when you visit https://www.google.com/maps/ , you will now get a browser notification for when it is time to leave. The notification works by drawing location information for your appointments from Google Calendar.