Whether it’s an important consumer application, a specialist app to solve a particular niche problem, or even a time-wasting game you can play on your phone, you can create a massively successful business if you build software that helps people. (Look at the rise of Slack—the team communication software that went from side project to billion-dollar company in just 2 years.)
Transcription is one of my part time jobs. I can do it conveniently from home and many of the clients are trainers or speakers. Having money and needing transcription services doesn’t imply you have a secretary. At my full time job the closest we have to a secretary is the CEO’s assistant. She books flights, plans travel, schedules meetings, transports his children, and helps with home renovations. She doesn’t have the time to sit and transcribe work when the CEO can send it to a company or freelance agent for a few dollars.
If you're serious about making money online, start a blog. Blogging is one of the easiest and most sustainable income sources. As long as the blog is setup the right way, in the right niche, with the right content targeted at the right audience, and the offer is complementary to the content, you could make a tremendous amount of passive income from a blog.