Airline Rebooking - this takes them forever
Any recurring visit business (Barbers, Nails, Dentist, Optometrists, Dispensaries, Restaurants, ...) customer engagement/tracking/service software
Any Job estimating business (painting, construction, masonry, welding ...)
Any billable hour business (freelancing, legal, babysitting, ...)
Consider walking down {Main|King} Street of your town, walking into each shop, and asking them about software they use and what they like and don't like about it. Attend a meeting of the Rotary or Chamber of Commerce and ask them.
The trick is that customer only sees problems and you only see solutions, so no customer will come to you proposing a solution to their problem, and you won't be successful guessing what problems the customer has. You have to go out and see for yourself and try to understand their pain points.