Software markets for solo developer [closed]

Question

I want to create something useful of my own which others can use it. This can be free or it can make a little money for sustaining its development and increase income little. However, when think about the market, I don't know what market is lacking applications, what types of domain can be possible for a solo developer or small development?

For example, I can develop small game for the smartphone market, with me as the programmer, another person is graphic designer and another person is music composer, to create a functional and playable game. Or what types of domain/market in web development are possible for a single developer to produce a web application?

Or should I include the forth person, business man to identify this for me? If you have experience on this, I would love and highly appreciate if you share for me and everyone.

EDIT: I want to do this as my part time job, not the main job until it's possible.