Google has been running Gmail Labs quite successfully for a while now. The idea is to get as many add-ons for Gmail out there as possible, but to make them optional. Some people might want to add their location and time zone to all their sent mail, some might not. Similarly others might want Google to ask them some math questions before it sends their emails, just to make sure they're in the right state of mind, other people want to be able to send all the drunk emails they want. If an application proves popular enough, it makes it out of Labs (Tasks just graduated today).
Now Google has said it will implement the same sort of process for additions to Google Calendar, which will now see a Labs tab when they log in. Under this tab there's a number of new features that are currently being tested for Google Calendar. At the moment, there are just six news Labs features for Google Calendar. These include Next Meeting, which shows you how much time you have to procrastinate, Free or Busy, which allows you to see which of your friends or coworkers are currently in meetings and World Clock which lets you keep track of different timezones when you schedule meetings. Similar to Gmail Labs, there's a feedback link for you to discuss these features and to suggest new ones.
Google will be adding new features all the time and developers interested in developing their own Labs app can grab the experimental API Google is releasing. Check out this post at the Google Code Blog for more information.