Add Collaborative Software section and Citadel, EGroupware, Kolab, SOGo and Zimbra servers.

README.md

@@ -6,6 +6,7 @@ A curated list of amazingly awesome open source sysadmin resources inspired by [
   * [Cloning](#cloning)
   * [Cloud Computing](#cloud-computing)
   * [Cloud Storage](#cloud-storage)
+  * [Collaborative software](#collaborative-software)
   * [Configuration Management Database](#configuration-management-database)
   * [Configuration Management](#configuration-management)
   * [Continuous Integration & Continuous Deployment](#continuous-integration--continuous-deployment)
@@ -82,6 +83,15 @@ A curated list of amazingly awesome open source sysadmin resources inspired by [
 * [ownCloud](http://owncloud.org) - Provides universal access to your files via the web, your computer or your mobile devices.
 * [Seafile](http://seafile.com) - Another Open Source Cloud Storage solution.
 
+## Collaborative software
+*Collaborative software or groupware suites.*
+
+* [Citadel/UX](http://www.citadel.org/) - Collaboration suite (messaging and groupware) that is descended from the Citadel family of programs.
+* [EGroupware](http://www.egroupware.org/) - Groupware software written in PHP.
+* [Kolab](www.kolab.org) - Another groupware suite.
+* [SOGo](http://www.sogo.nu/) -  Collaborative software server with a focus on simplicity and scalability.
+* [Zimbra](http://www.zimbra.com/community/) - Collaborative software suite, that includes an email server and web client.
+
 ## Configuration Management Database
 *Configuration management database (CMDB) software.*