This was the final project for my distributed application development course. We had to use the APIs for Google Calendar, Google Latitude and Gmail to build an app that allows users to schedule events with friends.
A Google Calendar is subscribed to by various people and whenever a new event is created the subscribers are emailed the details. The twist is that Latitude is used to decide whether a user is to be notified: a radius is defined, and if the user's last known position is within that radius the email is fired off. In the email there are three links: attending/not attending/don't know. When a user clicks one of the links the event in the Google Calendar is updated accordingly.
At the last moment it occurred to me a map of the itinerary between the user's location and the event's location would be awesome to include. I looked through the Google Maps API documentation and used the data we received from Latitude's API to generate a bird's eye view image of the route which we embed in the outgoing emails. Clicking on the image takes the user to the full route on Google Maps.