Idea: A web site / app where you write what you and your friends have/need, then via social-graph and match-making, you are introduced to other people via friends of friends, and on a set date you do the exchange, so you receive the apples from person A and send your oranges to person B. I used goods in this example, but it should be all but goods or money, it should be like favors, jobs, dates, fishing friend, etc.