It emulates an exchange server for the Palm, and syncs to gCal and gContacts.
A user has written a thorough configuration review:
Nuevasync: Over the Air Syncing of Calendar and Contacts for your iPhone or iPod Touch | The iLifeDon't miss the above in the setup.
... The first thing you really want to do is sync your current data back to Google. Open up iTunes, plug in your iPhone (or iPod touch) and click on your device and go to the “info tab” and check the sync contacts (make sure you say “Google Contacts” and enter your account info!) and sync calendar tab....
When you sync an iPhone to Exchange Server, you lose all the data on the phone -- unless it's moved to MobileMe or, through the back door, the the Exchange server source. Fun, eh?