Just a web-based app to schedule meetings for a list of people is relatively trivial. Of course for it to stay that way would require everybody using it. What I mean is, if you want the app to make everyone's calendars available to whoever is doing the scheduling, or to other users, then all the users have to keep their calendars up to date. (Or someone has to do it for them.)
This could be done in a couple of days if the specs really are:
* Every user will keep their personal calendar up to date
-- or --
* Someone keeps all calendars up to date
* There is an interface to schedule meetings that then appear on everyone's calendars
* A central user list that is owned by this application
* A central schedule that is owned by this application
But I assume there are plenty of people who already have preferred calendar/PIM/planning programs. Either they all convert to this new application, or the application will have to talk to some set of the currently-in-use apps for the lists, the schedules or both.
Anything that will involve multiple users instantly becomes as much a political decision as a technical one. If there is someone with the authority and the willingness to enforce a standard, this is fairly straightforward. If there isn't ...