“groovy mother...”

BusySync 2 will synchronize between Google Calendar and iCal in both directions. Unless Apple announce this exact feature at Macworld, I’ll be buying a copy forthwith.

Python library for working with Google’s GData web services (Calendar, Blogger, Picasa et al)

Ambient Devices online-prototype for a clock that displays your Google Calendar appointments in an at-a-glance stylee, including things like ambient colour-changing when it’s 10 minutes to the appointment.

Cunning use of Google Calender’s API to display system monitoring information.

Google Calendar has an Atompub-based API.

Greasemonkey script which finds hCal microformats embedded in webpages (such as Upcoming.org) and allows you to add events to your Google Calendar with one click.