CalDAV Clients/Outlook/iCal4OL

This is a Windows only program you have to buy, but there is also a trial version available.

iCal4OL is a program for smart importing (syncing!), exporting and subscribing (as Remote Calendars) ICAL files (*.ics) and feeds in Outlook.

A perfect 2-Way Synchronization with Google Calendar and CalDAV/CardDAV Solutions is integrated (events, tasks & contacts).

(AllConnected4, Bedework, Chandler Cosmo, Citadel, Communigate Pro, Darwin CalendarServer, DAViCal, DavMail, EGroupware, GroupOffice Prof, Icewarp, Kerio, maxVis, MobileMe, Scalix, Smartermail, SOGo, Tobit, Yahoo, Zarafa, Zimbra, ..)

Incremental synchronization in background is possible e.g. every 5 minutes. You can use multiple configuration files (*.ini) to sync multiple calendars.

http://ical.gutentag.ch/

Tested with DAViCal 0.9.4 - 1.0.2 (CardDAV since 0.9.9.3)

Configuration: Use the CalDAV Autoconfiguration Assistant on tab "Who" called [Others]. It will configure all collections automatically (Your own calendar and contacts collection, and delegations defined as calendar-proxy-read/-write).