You can sell you advice and knowledge to many people. You don’t have to be super expert in one domain to become a consultant or teacher, you just have to be better than your student or client. Anyone with a core competitive skill can become a consultant and find clients online. For example, if you are a legal or finance professional, then you can make your website, and start attracting clients online.
Every product cannot be defined by its market niche. The niche market is highly specialized, and aiming to survive among the competition from numerous super companies. Even established companies create products for different niches; Hewlett-Packard has all-in-one machines for printing, scanning and faxing targeted for the home office niche, while at the same time having separate machines with one of these functions for big businesses.