Google is testing a new feature that mimics something Yahoo already partially has: Google Links, i.e. links to your favourite Google services, that will follow you everywhere you go on Google.com.
While looking at these services, you will see something weird: what is Google CL2? The famous Google Calendar, announced since more than a year? If you click on the link, you get "The page you requested is invalid".
Update: Google Calendar screenshots
5 minutes ago