• Integrated Email Management
  
• Contact Management
• Forum
• Simple Documentmanagement
• Linklists or uncategorized information

Group Office

+ Forum extension
+ Big community in Austria and Japan
+ Calendar provides iCal support
+ friendly, clear user interface
+ Projectmanagement feature
+ Notes
+ German language support
+ Common folder to share data between users

phpGroupWare

+ Forum
+ Huuuge feature & extension base
+ Extensive projectmanagement
+ Knowledgebase (for e.g. glossary)
- Insufficient file management, no filetypes – No WYSIWYG editor (!)
- Quite confusing UI (e.g. messenger) and partly ineffectual implemented

eGroupWare (Fork of phpGroupWare)

- No forum
- Very project management aligned
- No WYSIWYG editor and existing editor lacks of functionality

PHProjekt

+ Incredible feature set (Even chat via web browser)
- Nerdy UI with endless long forms is definitely not very sexy
- Cross browser issues: Context menu doesn’t work correctly in Firefox
- Filemanagement very cumbersome

dotproject

+ iCal export
+ Files can be attached to tasks
+ Outboard, for managing
+ Quite simple UI (colours could be improved)
- No Email management. Emails have to be send via an external client
- File creation via upload only

phpCollap

- No live demo found
- Not modular (at the moment)
- Early project state

moreGroupWare

+ “Outlook like” Email management
+ Problems on Mac
+ Early release (0.7.4)
- Login problems with some browsers (FF 2/Mac)
- No WYSIWYG Editor, plain text files only

In the end the big code & user base of Group Office and the fact that it met all our requirements from the beginning made a clear winner. Please note: that the listed projects may have been updated in the meantime and features may have changed.

Additional Sources:
List of collaborative software (Wikipedia)