Best plugin for scheduling appointments?

Yes. When a user who creates their schedule receives a booking from a user in another time zone both users receive emails confirming the date and time in their respective timezone.

Users who are in a different timezone than the schedule creator will view the available time slots in their relative time zone. So a user who creates a schedule who is in Indochina timezone, is booked by a user in EST time zone (12 hour difference) the schedule creator who listed Monday 10AM availability will be displayed as Sunday 10PM to the user booking a meeting from EST time zone.