Lotus Domino for Linux  
   Lotus Notes/Domino R5 for Linux/x86 - a Groupware Client/Server
   http://www.lotus.com/home.nsf/welcome/dominolinux/

iOffice2000  
   A full featured (commercial) web based groupware suite that aims to improve communication and information sharing for groups.
   http://www.neoint.com/ioffice2000/

phpGroupware  
   Open Source collaboration software written in PHP. Includes features such as email, shared calendar, task list, address book, inventory, trouble ticket system, and many others.
   http://www.phpgroupware.org

Domino for Linux  
   Linux and information from Lotus Development Corporation staff about how to configure, design and rollout Lotus Domino R5 for the Linux Platform.
   http://www.lotus.com/products/r5web.nsf/webpi/Domino+for+Linux?opendocument

groupware PHProjekt  
   Open source groupware suite with calendar, project management, request tracker and 12 other modules. Supports more than 20 languages. Requires mysql, oracle, postgres, interbase, ms-sql or informix db.
   http://PHProjekt.com

e-Bills - billing application for Linux  
   The home of e-Bills, as web-enabled billing application for Linux using PHP and MySQL. Contains downloads and application information.
   http://www.asplen.co.uk/billing

twig  
   An opensource groupware/intranet application focusing on simplicity and being cross-platform / browser-independent.
   http://twig.screwdriver.net