Exchange Server replacement?

[Simon Clayton]

I have a customer who uses Outlook lots.  They 
haven't got an Exchange Server and so cannot 
share their contacts and diaries.

They have asked us to find out how much it 
would cost to install Exchange Server on their
existing NT platform.

So, the question is - is there any software 
that will run on FreeBSD that will allow users
to share Outlook diaries/contacts without having
an Exchange Server?

Thanks in advance for any help

Simon Clayton
Reference Technology Ltd