"Sunbird, Mozilla's calendar application, supports extensions
just as Firefox and Thunderbird do. What kind of extensions work
with a calendar? How about being able to get a weather forecast
when you're setting up a golf date, or exporting your desktop
calendar to a Web service?
"World Weather+ is a great extension that grabs weather data
from the Weather Channel. It displays the current conditions on the
left side of Sunbird, below the task section..."