It is important to know which features belong to your product and which don't. Intercom has made a good mini-site about the subject: "A great product manager knows how to say no to ideas that don’t serve their product, their vision, or their customers."
We decided to hold a two-day hackathon to find out what we could build. We organized into three teams, each with the same goal: building a product that somehow would promote its users' health. This is a short introduction to what we built.