Google today announced that they were no longer switching the CalDAV API to partner only. In March they announced that the API would no longer be public, but would instead only be available to a few large partners however today they announced that they would be reversing this decision. As well as keeping CalDav public they also announced that they would also be making a CardDav public as well.
CalDAV is the API for calendar data across the web with CardDAV being the API for contact information.
The news was announced on Googles developer blog today