The Day Planner widget that comes with the Yahoo! Widget Engine (a.k.a. Konfabulator) can work with iCalendar (ICAL) files, but this feature has been hidden in the Windows platform since Mozilla Sunbird stopped using iCalendar files (.ics) for storing calendar data.
Google Calendar makes a private link to your calendars, in various formats, including ICAL. To use it with Yahoo! Day Planner widget (which looks a lot better than Google Desktop Gadgets, IMO), you have to do 2 things:
- Find a way to periodically download the GCal .ics file from the Internet to a file on your computer.
- Hack the widget to use the .ics file for calender info.
Now, to periodically download the .ics file... You can get your private URL for the .ics file under Settings in Google Calendar (more info). I made an AutoHotkey script to download it periodically, but I imagine there are a lot of little utilities that can periodically download a file from the Internet. Whatever you set up, when you start Yahoo Widgets again, you'll be prompted for the directory where the .ics file you want to use is located.
Update: I modified the Day Planner widget to make it more friendly to iCalendar files. I used the Widget Converter widget to convert the Day Planner.widget to a folder. I then edited PIMp.kon in Wordpad.