This isn't exactly what you're asking, but consultancies that produce mobile apps on behalf of clients can see significant revenue. This is particularly true for apps that require user-to-user interaction or other functionality requiring a decent amount of backend code.
Unlike websites, which are largely commoditized by big players, custom apps still fetch large sums. The pros in this space charge project-based (or at least per diem) rates, so you'll need to be good at estimating your work.
Unlike websites, which are largely commoditized by big players, custom apps still fetch large sums. The pros in this space charge project-based (or at least per diem) rates, so you'll need to be good at estimating your work.