From W3C Wiki
Centralized calendaring and scheduling are somewhat mature. Exchange server basically works. So does yahoo calendar.
But what if I want to schedule a meeting between three people in my company, four in a company that uses lotus notes, three that use yahoo calendar, two that use PDAs, and one that uses emacs diary?
I need a scalable calendaring and scheduling solution; scalable in the sense of AnarchicScalability of the Web.
more on reconcilliation rituals (PaperTrail style).