Program to share/schedule outlook calendars online?

[Pandamonium]

Google calendar is great if you only want to share your calendar with a finite number of users. But what if I would like my schedule to be visible (maybe without details, but at least an hour-by-hour listing of whether I have free time slots available) to the general public. Then, someone could request an appointment and the website would send some kind of feedback to my machine, which would forward the request to my outlook. Upon my approval, the time slot would be shown as unavailable online, in real time. Is there something that does this?