Spanning Sync keeps your Google Calendar and your Mac’s iCalendar up to date with each other, eliminating the need for you to manage separate calendars. After you’ve set up Spanning Sync, changes made to Google Calendar will show up in iCal, and changes made in iCal will appear in Google Calendar.
Additional features of Spanning Sync include support for one set of calendars on multiple Macs, and compatibility with mobile devices such as iPods and cell phones. With Spanning Sync, you can one calendar to rule all your computers and gadgets.
Spanning Sync is free for 15 days, and then costs either $25 for a year, or $65 for unlimited use. The software comes with the recommendation of heavy hitters like The Unofficial Apple Weblog, Wired News, Insanely Mac, Download Squad, and ZDNet.