The Kolab groupware is a great open source alternative to well known closed source groupware solutions. For example, the Kolab groupware has most of the features of Google Mail including mail, calendar, contacts and supports sharing of those entries between users. Since Kolab 3.1 there is also CalDAV and CardDAV support included via a SabreDAV based protocol layer called iRony. This turns Kolab into a CalDAV/iCAL server that enables synchronization of Kolab stored calendars and contacts with any CalDAV/CardDAV supporting device, e.g. Android or iOS based smartphones and tablets. However, Kolab still has no CalDAV/iCAL client support, meaning that adding external calendar resources such as holiday calendars, birthday calendars, shared Google Calendars or any kind of external CalDAV/iCAL calendars is not possible so far. Therefore

Kolab is a free groupware based on Postfix, Cyrus IMAP and Roundcube. The groupware includes email, calendars, addressbooks, task management and a wide variety of clients. Since version 3.1 Kolab also supports the standardized CalDAV and CardDAV protocols so that all data can be synced to a phone, tablet or any CalDAV/iCAL client. More than enough to have a closer look. Kolab is community driven and has enterprise support by Kolab Systems AG. Next to the enterprise version, they also provide community packages for RHEL and CentOS. The source code is available from their Git repositories. An openSUSE Build Service provides additional testing packages for Debian, Fedora, OpenSUSE and Ubuntu. Unfortunately, the Gentoo support for Kolab seemed to starve for some reason. We only found