Groupware Options on Mixed Networks

[Jason Greenwood]

Ok, all, here's your chance to shine!

We run a mixed network of Macs (OS9 and X), Winders and my sole Linux 
box. =) What we would like to do is set up a networked 
Groupware/Collaboration/Calendaring/project management system that can 
be shared amongst them all, running on a Linux server. I know there are 
options like Kroupware and one of the proprietary Samsung and Ximian 
offerings but I want to know what you all have tried and what works! We 
want to have our calendars stored on the servers and open for anyone to 
view and modify. We want to leave messages on the server like a message 
box for each other and other collaboration "stuff." I know the normal 
solution on Winders networks is bla bla Outlook+Exchange but that is not 
an option as long as I work here... =)

Perhaps there are web based/Java options I am missing?? Any and all 
ideas welcomed.

Cheers

Jason