Actually it is hard to tell. Every application is simple from start, but then expand. You could say Instagram is simple - create a user, upload a picture which

Actually it is hard to tell. Every application is simple from start, but then expand. You could say Instagram is simple - create a user, upload a picture which people can see if they choose to add you as a friend. Simple at first, but then the application evolves to filters and sophticated algorithms for finding best content