My colleague just managed to get Oracle Beehive running in our labs, so I went ahead to play around with this Collaboration Suite.
I'm always curious how well is Outlook Connector being supported.
•Microsoft Windows XP: Home or Professional
•Microsoft Windows Vista: Home, Business, or Ultimate
•Microsoft Windows 2003 Server
•Microsoft Windows 2000: Home or Professional
•Microsoft Outlook 2007 (with Service Pack 2)
•Microsoft Outlook 2003 (with Service Pack 3)
•Microsoft Outlook 2002 (with Service Pack 3)
•Microsoft Outlook 2000 (with Service Pack 3)
Much more comprehensive than what AXIGEN and SUN have to offer. See here.
However, it is still not the complete list. My favorite Windows 7 family is still not supported. It'll take time since Windows 7 has been out in the market for only a while.