This is at the beginning stages, and Eventbrite teased the concept to members of the media in New York on Tuesday. Basically, 'At the Door' revolves around an iPad app, a credit card swiper, and a ticket printer, all of which can be quickly assembled at the venue and moved on a whim. The system can process 400 tickets an hour, and even functions while offline (though online processing introduces far better features).
This is all part of a broader initiative dubbed Eventbrite Box Office, and the company is testing the beta concept. But a traditional venue is not required for this to work; instead, the ticketing action can happen around any event, wherever that might be.