pagetta
I use
VCalendar. Did not see it on the link suggested above. It runs under PHP/SQL, etc. Did some research and it seems to be flexible enough for my use, pretty easy to implement and have users keep up to date.
I have it running for personal matters. If you would like to see it in action, shoot me a note!
Located on sourceforge here:
https://sourceforge.net/projects/virtualcalendar