Attendio helps you avoid that dreaded circular conversation: "What do you want to do tonight?"---"I don't know, what do you want to do?"---and so on.
More specifically, Attendio is a social-events discovery service that continuously feeds events directly to a calendar program based on specified interests and geographic location.
Launching here at Demo 07, Attendio is not shy about how new it is--its tagline is "seriously beta." (Speaking of names here at Demo, can we talk about that? Attendio, Yodio, Vringo ... the names sound to me like a series of toys for freakishly smart children.)
Anyway, users pick their interest--hockey, electronica, whatever--and location. Choose the preferred calendar program, and any event fitting the selected interests will continuously show up on the appropriate calendar date. From the calendared item, users can buy tickets and notify friends that might be interested in attending as well.
Each user has a profile that compiles their chosen interests and events that they would recommend. As a bonus, if you're out on the town and at a loss for where to go next, Attendio registered users can send a text message that will retrieve all Attendio-recommended events sitting on their calendar.