[plt-scheme] plt calendar application with ical format

Hi,

I wonder if there is any plt calendar application to use / build on that
might run on a web server?

The thing is, I might be allowed to use scheme at work (which would be
far from self-evident ;-) ) to replace an old php script that based on
an algorithm computes and inserts data into a given, indepentdently
existing online calendar (up till now, part of a php cms).

Now the requirements would be that the script operate on a file in ical
format, which is also actively manipulated by different users. So the
calendar application itself should run on some machine behind a web
server, and after a first search it seemed like this was not a problem -
install something like "phpicalendar" and that's it. But it turned out
that "phpicalendar" can only show data and does not allow changes.

Now building a calendar from scratch with scheme would certainly exceed
the time allocated for this (minor and administrative only) task, so I'd
like to know if there is already a graphical calendar tool which works
with (or can be adjusted to work with) the ical format and could run
behind a web server?

(I saw the ical parsing library on Planet, but unfortunately I need the
whole calendar now...)

Thanks a lot in advance,
Sigrid