Centralized Identity Management Solutions

OpenSource Directory Servers
* OpenLDAP – http://openldap.org
* 389-DS – http://directory.fedoraproject.org
* Apache-DS – http://directory.apache.org
* OpenDS – http://opends.java.net

Single Sign On
* MIT Kerberos – http://web.mit.edu/kerberos/

Domain Name Service
* ISC Bind – https://www.isc.org/software/bind
* PowerDNS – http://www.powerdns.com

DHCP Server
* ISC DHCP – http://www.isc.org/software/dhcp

Version Control System
* Git – http://git-scm.org
* Subversion – http://subversion.apache.org
* Mercurial – http://mercurial.selenic.com
* Bazaar – http://bazaar.canonical.com

Backup Software
* Amanda – http://www.amanda.org
* Bacula – http://www.bacula.org

Central Repository Server
* DebMirror for Debian – https://help.ubuntu.com/community/Debmirror
* Rsync – Usually used for mirroring – http://rsync.samba.org/

Antivirus
* ClamAV – http://clamav.net

Network Imaging Solution
* Clonezilla – http://clonezilla.org
* fog – http://www.fogproject.org
* G4L – http://g4l.sourceforge.net

Software and Hardware Inventory
* OpenAudit – http://www.open-audit.org
* OCSInventory – http://www.ocsinventory-ng.org
* FusionInventory – http://www.fusioninventory.org
* GLPI – http://www.glpi-project.org
* Tracmor – http://www.tracmor.com

Content Management System
* Alfresco – http://www.alfresco.com
* Joomla – http://www.joomla.org
* Drupal – http://www.drupal.org
* Typo3 – http://typo3.org
* Concrete5 – http://www.concrete5.org
* Plone – http://plone.org
* OpenCMS – http://www.opencms.org
* Locomotive – http://locomotivecms.com

Network Monitoring and Dashboard
* Nagios – http://nagios.org
* Centreon – http://www.centreon.com
* Icinga – http://www.icinga.org
* Ninja – http://www.op5.org/community/plugin-inventory/op5-projects/ninja
* OpenNMS – http://opennms.org
* Zenoss – http://community.zenoss.org/index.jspa
* Zabbix – http://www.zabbix.org

Mail Servers
* Zimbra ZCS – http://www.zimbra.com/downloads/os-downloads.html
* iRedOS – http://www.iredmail.org/
* DeepRootLinux – http://www.deeproot.in

Reverse Proxy Servers and Web Servers
* Apache Httpd – http://httpd.apache.org
* Nginx – http://nginx.org/en
* Lighttpd – http://www.lighttpd.net
* Varnish (proxy only) – http://www.varnish-cache.org

Web Proxy Server
* Squid Proxy Server – http://www.squid-cache.org

Network Access Control
* Packetfence – http://packetfence.org

Management Tools

* Ovirt – http://ovirt.org
* Karesansui – http://karesansui-project.info/
* Archiphel – http://archipelproject.org/
* Ganeti – http://code.google.com/p/ganeti/

Cloud Software

Iaas
* Openstack – http://www.openstack.org
* Cloudstack – http://www.cloudstack.org
* Eucalyptus – http://www.eucalyptus.org

PaaS
* OpenShift Origin – https://openshift.redhat.com/community/open-source
* WSO2 Stratos – http://wso2.com/cloud/stratos
* CloudFoundry – http://www.cloudfoundry.org

Virtual Private Network
* OpenVPN – http://openvpn.net

VOIP
* Asterisk – http://www.asterisk.org
* FreeSwitch – http://www.freeswitch.org

Chat Server
* Ejabberd – http://ejabberd.org
* Openfire – www.igniterealtime.org/projects/openfire/

Team Collaboration Tools
* OpenAtrium – http://www.openatrium.org
* Redmine – http://redmine.org
* Teambox – http://teambox.com

Security Tools
* OpenVAS – http://www.openvas.org
* Snort – http://www.snort.org

Configuration Management Tools
* Puppet – http://puppetlabs.com
* Chef – http://opscode.com/chef
* Cfengine – http://cfengine.com
* Salt – http://saltstack.org