You actually need a domain expert, or to become one yourself, within some field to even begin to know what the current issues faced are, what technologies or products are already in use, and what kind of solution would be acceptable in the market. The balance then of finding the solution is actually much more 50/50 than a lot of tech people want to believe - its not just them sailing down on a cloud and delivering some perfect pre-made solution.
Usually I find these people through my friends or family. You basically have to sit down and interview them, and have a back and forth to find what kind of things would or wouldn't work in their industries. I don't think theres some magic bullet to finding all untapped markets.
Two niches I encountered, independent music schools, garden centres/nurseries.
So you're not going to bring a flourish just by bringing tech, they already have it. But can it be done better? Hell yes.
Can you make a business model out of doing it better?
...I don't know. In my country, that's a lot of start-ups that target agriculture, and deliver some good results, but then find out that farmers are risk adverse when it comes to new spending.
An old colleague developed fantastic software for managing hives, and then found that the beta testing apiarists who loved his software were even more risk adverse than farmers.
But yeah, if you want to target a niche, you need a partner who not only knows the problem domain, but the market/social network, and has good relationships, as sales will initially be word of mouth.
- customer support
- health/beauty/nutrition advice
- "content creation" ie blog post SEO spam
- tax/legal
- digitizing, managing, filing out paperwork
- supermarket cashiers
- government bureocracy of any kind