If you're looking to have only one calendar that everybody uses (no personal/user specific calendars) that'd be a pretty simple script to write. You could do it with a single SQL table if you wanted to; Date, Time, Duration, Description. Pull out the results for whatever month your viewing and build the interface however you please.

To answer your question though, no I'm not aware of such a script, but it seems feasible you could probably find something similar at any of the various script repositories out there.
-m