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.)
Blogging is still a viable online business idea, and one with as much potential as ever. Just make sure that you start a blog on something that people actually want to read about. If that happens to be something you’re passionate about that’s great. But you need to understand that it’s way easier to monetize a blog about organic dog food than it is to make money from a blog about obscure literary fiction.