After two years of hard work, the Kolab Groupware Project has released Kolab 2. It allows for sharing of personal folders, calendars and contacts and comes with improved spam and anti-virus capabilities. With Kolab 2 installation is now an easy two-step process, and the admin web interface has many improvements. KDE recently started supplying Kolab for its contributors. KDE Kontact is the project's official groupware client on GNU/Linux and Unix derivates.
If you do not have KDE 3.4.1 installed and still want to try Kolab, the Kolab folks have provided a special version of Kontact that will work with KDE 3.2 and higher.
The unique concept of storing everything in MIME structures on the Cyrus IMAP server allows for on-the-fly-backup. As the client performs most of the groupware tasks, Kolab is extremely scaleable. It is built entirely on Free Software.
Windows users can use the Toltec plugin to turn Outlook in a fully-fledged Kolab client. A web-based interface to mail, calendar and contacts based on the Horde framework is in beta-stage and will be released later.