"TimeTrade, Doodle, WhenisGood do it, it should be interoperable - scheduling driven by the attendees who get to vote on the best times and locations for group events"

Consensus scheduling involves using a poll-based or vote-based mechanism to determine the date, time, location of an event or a task. This has been implemented by several vendors in their own systems but should be available and interoperable within mainstream scheduling. VPOLL is an additional iCalendar and iTIP component designed to allow the implementation of consensus scheduling with any system and client. TC FREEBUSY.

Details: Consensus Scheduling (VPOLL)