There used to be Idea Sunday on HN https://hn.algolia.com/?query=idea%20sunday The general rule is: solve somebody's problem (and thus create value for that person). And it doesn't have to be a problem millions of people have. A friend focused on supply chain optimization (webapp) for dental factories (not sure that's the right word). Another build a mobile app for pharmacies. I tend to tell people to talk to business men/women of traditional (boring?) industries.