"A feedback loop involves four distinct stages. First comes the data: A behavior must be measured, captured, and stored. This is the evidence stage. Second, the information must be relayed to the individual, not in the raw-data form in which it was captured but in a context that makes it emotionally resonant. This is the relevance stage. But even compelling information is useless if we don’t know what to make of it, so we need a third stage: consequence. The information must illuminate one or more paths ahead. And finally, the fourth stage: action. There must be a clear moment when the individual can recalibrate a behavior, make a choice, and act. Then that action is measured, and the feedback loop can run once more, every action stimulating new behaviors that inch us closer to our goals." http://www.wired.com/magazine/2011/06/ff_feedbackloop/
Apps can live inside or outside the Locker. They can be anything from a tiny utility related to a specific type of data, to a full blown platrom within themselves.
If you would like to discuss app design and development further, come visit us on irc.freenode.net on #lockerproject.