Looks to me like a fairly straightforward web app
If no one has already done something that includes that -- and several packages have calendar componenets, see PHPGroupWare, Twig and a few others -- that's an easy feature set. Like I said, getting the buy-in that all data is owned by this app, meaning it's the primary source for scheduling, is the hard part. If you've got that, the implementation can be done in under a man-week.
Take a look at [link|http://freshmeat.net|freshmeat] and [link|http://sf.net|sourceforge] to see if there's an existing package that does what you need. If not, let me know and I'll see what I can come up with.
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