Bolster Suite → BolsterCal Appointment Calendar:
BolsterCAL: Appointment Calendar Server
provides easy to use iCal compliant Appointment Calendar.
Each user can manage appointments for a single day, recurring appointments, multiple days (including vacation).
Includes mouse-over appointment details on the email dashboard, multiple views and more.
SPAM filtered auto responder responds to every approved email, and places every responded email in the user's Sent folder, and much more.