GCALDaemon – Calendar Synchronizer
http://gcaldaemon.sourceforge.net/index.html

GCALDaemon is an OS-independent Java program that offers two-way synchronization between Google Calendar and various iCalalendar compatible calendar applications. GCALDaemon is primarily designed as a calendar synchronizer but it can also be used as a Gmail notifier, Address Book importer, Gmail terminal and RSS feed converter. This has been added to the tools section of Research Resources Subject Tracer™ Information Blog.