Thunderbird Add-on: Sync Kolab

The Sync Kolab extension for the Thunderbird email client allows you to set up synchronization with imap servers for both calendar and address books.

This is extremely helpful for those that are looking for portability and when it comes to working on email from multiple different points of entry. Now this allows not only your server-side to be at any point, but your local ends also to be synchronized in case you lose connectivity or something. And using iCal's calendar format is pretty spectacular, since that's basically the one thing that Outlook had on open-source type software.