Group ware/outlook packages?

[Sam Mulvey]

Hello!

I've got a project where a group of people would like to have some  
sort of group ware and project managment system... their go to  
application in the past has been outlook and exchange, and this time  
they'd like to go with something else.   What I'm looking for is  
something web based that can sync or at least talk to Mozilla  
Calendar and Apple iCal, since they'd prefer to have some application  
to use rather than logging into a web page.

There are a couple projects out there, but I'm not sure what's better  
supported or more robust or whatnot-- there are a lot of  
semicommercial players out there.

If anyone has any insight or advice, I'd really appreciate it.

-Sam