No, not that hard, M, but also, as far as I can see, not much use I fear! Nearly all of the ones I have looked at in your 'link' are 'apps' for mobis, and I specifically do NOT want an alternative for the Google calendar since that does not do what I asked in post #1.
To repeat - needs:
FREE!
Username/password access for users to add content
Web based (CGI/PHP/Perl/????) as required.