[Dovecot] Recommended Groupware?

[it-dovecot at ml.epigenomics.com]

Hi,

is there a recommended groupware (email + calendar + address book +
syncing with mobile devices) on top of an existing dovecot installation?

Most existing commercially supported groupwares come with their own mail
storage engine. I would like to keep dovecot as the email storage engine
because of the maildir format which greatly helps with backup & restore.

Regards
-- 
Robert Sander