One route to success is to take some other domain that you have expertise in, that most software devs aren't familiar with. Come up with an application that solves a problem in that domain, then market to those people. Here's a simple example (this probably won't make any money, but it is good for illustrative purposes). If you look at an egg carton, there is a sell by date on there, but it doesn't list the date that…
If you have a family with X family members, and each person has a loyalty number for Y airlines and Z hotels, that starts to become a lot to keep track of. Wouldn't it be great to see all of your loyalty accounts on a single page? Then you could have cool graphs, growth rates over time, etc. Also a tool to make sure that all family members are getting credit for all of their miles/stays.