EWS-Client is a module that acts as a client to the Microsoft Exchange Web Services API. From it you can access calendar and contact entries in a nicely abstracted fashion. Query results are generally available in an iterator and convenience methods exist to access the properties of each entry.
DavMail is a POP/IMAP/SMTP/Caldav/Carddav/LDAP exchange gateway allowing users to use any email/calendar client (e.g. Thunderbird with Lightning or Apple iCal) with an Exchange server, even from the Internet or behind a firewall through Outlook Web Access. DavMail now includes an LDAP gateway to Exchange global address book and user personal contacts to allow recipient address completion in the mail compose window, and full calendar support with attendees free/busy display.