Open source collaboration softwares

Standard client–server software

Access Grid, for audio and video based collaboration

Citadel/UX, with support for native groupware clients (Kontact, Novell Evolution, Microsoft Outlook) and web interface

Cyn.in

eGroupWare, with support for native groupware clients (Kontact, Novell Evolution, Microsoft Outlook) and web interface

Group-Office groupware and CRM

Kolab, various native PIM clients

LibreSource

OpenGroupware.org

phpGroupWare

Scalix

SOGo, integrated email, calendaring with Apple iCal, Mozilla Thunderbird and native Outlook compatibility

Spicebird, integrated email, calendaring and chat; Windows and Linux

Teambox, Basecamp-style project management software with focus on GTD task management and conversations. (Only V3 and prior are open-source.)

Zarafa

Zimbra

Groupware: Web based software

Bricolage, content management system

Collabtive, web-based project management software

BigBlueButton, Web meetings

DotNetNuke, also called DNN: module based, evolved from ASP 1.0 demo applications

eGroupWare, a free open source groupware software intended for businesses from small to enterprises
EtherPad, collaborative drafting with chat

Feng Office Community Edition

Group-Office, Web based groupware for sharing calendars, files, e-mail, CRM, Projects, Mobile Synchronization and much more.
Horde

Jumper 2.0, collaborative search engine and knowledge management platform

Kolab Groupware, integrated Roundcube web frontend

Kune, collaborative federated social network, based on Apache Wave

FusionForge, has wiki, forums, mailing lists, FTP, SSH, subdomains, hosting, email alias, backups, CVS/SVN, task management

MediaWiki, which provides core content management and integrates with many other tools via extensions

OpenBroadcaster Radio station in a box

phpGroupWare

Simple Groupware

SOGo, integrated email, calendaring with Apple iCal, Mozilla Thunderbird and native Outlook 

compatibility

Tiki Wiki CMS Groupware, has wiki, forums, calendar, ticket system, workflow engine

Tine 2.0

Tonido, free collaborative software with workspace synchronizing, Web access from personal desktop; cross-platform

Zarafa, full MAPI MS Exchange replacement for Linux, GPL+proprietary

Zimbra

Other

Alfresco, enterprise content management system: document management, workflow, and portal

Drupal Framework, open source content management framework: document management, web pages, attachments, forums, photos, social profiles, collaboration tools

eXo Platform, suite for enterprise content management (DMS, WCM, workflow) and collaboration (mail, instant messaging, shared calendars, address books)

KnowledgeTree, document management system: document management, workflow, portal

Liferay Enterprise Portal, open source enterprise portal: document management, wiki, social tools, workflow

LogicalDOC, document management system: document management, workflow

MySource Matrix, enterprise Web content management system from Squiz

Nuxeo EP, enterprise content management system: document management, workflow

OpenKM, open source document management system: document management

ResourceSpace, digital asset management