As well as the more basic iCal support, we are now running a calendaring server system called Davical. It is fully compatible with the Mac Calendar, iPhone's and iPads, and Lightning, the Thunderbird email client plug-in. We have also found an non-free Outlook plug-in called iCal4OL which costs about £15 per user. - This feature is part of the Base Install Module and was added to all our systems on 31st December 2012.