The Department of Informatics uses almost exclusively open source software in general and Debian/GNU Linux in particular on their server infrastructure. Currently we run Debian on around 20 physical and 40 virtual machines (KVM). Figures which are constantly growing.
Services provided on these machines include DHCP, LDAP, SMTP, IMAP, webmail, mailing lists, CalDAV, Samba, redundant storage, backup, Subversion and Git repositories, web proxy, Drupal and Joomla websites, MediaWiki, Tomcat, PostgreSQL and MySQL, configuration management and inventory. Migration of DNS on to Debian machines is planned, after which our central IT services will be entirely Debian-based.
The most important reasons to us for using Debian is its stability, security and upgradeability. Furthermore, we also like its flexibility when it comes to mixing in packages from testing or unstable to systems running Debian stable. This enable us to profit both from the stability of Debian (based on the conservativeness of Debian stable) and to be up to the state of the art for exactly those packages where it is required. Additionally, Debian is among the most complete distributions, i.e. most of the software we need is already packaged for Debian.