FOSS, Shared Calendars, & Outlook

[Aaron O'Hara]

All,

Is anybody aware of software that enables Outlook users and non-Outlook
users (like Evolution) to share calendar information using a Linux-based
server?  It seems as though all companies that offer this have closed
source MAPI connectors for Outlook.  If there was a totally free
solution that enabled my Outlook users to share calendars, I'd be all
over it.

Linux based products are out there, like exchange4linux, CommuniGate
Pro, SuSE Mail Server, but they have a per-seat cost around USD$600+ for
a small office.  Searches in Freshmeat don't turn up anything.

-- Aaron