Carry your Google Calendar in your pocket! GCalSync is an open source application that lets you do a two-way synchronization between Google Calendar and your phone's built-in calendar. Download events to your phone, or add an event on your phone and upload it to Google Calendar.

Features 

• Download events from Google Calendar to your phone's calendar
• Upload events created on the phone
• If an event has been changed in Google Calendar since last sync it will be updated on the phone
• Specify time period you want to sync as number of past days (default: 1) and number of future days (default 30)

GCalSync is still in its early stages, so expect some rough edges. Known limitations:

• If an event has been changed on the phone, the changes will not be uploaded to Google Calendar
• Reminders not supported
• Recurring events are treated as multiple events