This is a test and demonstration of Any+Time jQuery Widget, which was one of the tools covered in my "Quick Review of jQuery Date/Time Widgets". The demo highlights the following features in particular:
The demo constructs Google Calendar Event URLs without needing to put an event in your own calendar. It basically just stuffs the details you enter below into a google.com/calendar/event with all the correct parameter encoding. You can then put the link in an email or a website. Other people can then use the link to create the event in their own Google Calendar.
The Google Calendar Event Publisher Guide has a similar tool. The official documentation for the google.com/calendar/event parameters is available here The LifeHacker article Supercharge Google Reader with Send To Links was the main inspiration for this tool, and references some good sources of information.