Question

I’m searching for a multiuser web-based calendar system that supports multiple users.
I’m looking for these features:

• Multiple users
• Two user groups: First group is allowed to see events, the second group can create and edit events
• The events should be stored in a mysql database or a file
• The system has to be (very) easy to use. It will be used by non-technical users
• Ideally it should be integrated in wordpress, but thats a nice-to-have

If you know something like this please let me know.

edit (concerning the google apps comment):
the calendar should be hosted on an existing website

Answer 1

I totally understand your issue with your client. I had the same issue explaining to my boss that Google docs were more secure then a shared excel spread sheet. This is what finally convinced her, I pointed her to the attacks against Google from China. –source http://www.wired.com/threatlevel/2010/01/operation-aurora/

I then explained that it would take billions of dollars in R&D to even come close to the level of security that Google provides.

If that doesn’t work I would suggest using one of the many many OS calendars out there (http://arshaw.com/fullcalendar/ looks awesome) and go from there.