Ask HN: What are the least competitive consumer and enterprise markets?
Beware: if there are markets that appear uncompetitive, there is a damn good reason for it.  And it's never becaues no-one thought to look there.  If you do find uncompetitive markets, it'll most likely be because someone has regulatory capture, or there is something preventing new entrants, high barriers to entry, or the cost of user acquisition is simply too high for new entrants.