This has become a popular business model for online entrepreneurs over the past several years, and will probably just continue to grow in popularity. The best thing about selling online courses is that once you do the up-front work in creating the course and setting up your marketing strategy, you can get paid over and over again for work you do once.
If you have a background in a specific field, you may find there is a demand for writing industry papers in your area of expertise. For example, there are often adverts for doctors, lawyers, nutritionists, and business experts from particular niches, to write white papers on different subject areas. These are well paid jobs that you will need to stake your reputation on, but that can often be worked on from the comfort of your own home.
Another thing to consider is that even if you break even on the first sale, you're still winning. All you need to do is create more content about other problems that target market may have following the same principle and queue them one after the other. For example if we target women that want to lose weight they may also have wrinkle problems, digestion problems, diabetes, aging problems etc. We can easily create a chain of issues we run the email list through, let them opt in for what matches their issues and make several sales to that audience.
But don't make the mistake of thinking this will be a passive source of income—you're on call whenever you have a guest and you'll always need to keep the place clean for incoming visitors. On top of just renting on Airbnb, consider offering your guests paid add-ons, like Lauren Gheysens', Royal Day Out in London, England—where she gives visitors a local's only tour of the city, complete with bespoke 18th century costumes.
Now, I know what you’re thinking. Most of the software and apps you use on a regular basis are made by massive companies or established development studios. Well, yes. But many successful apps, particularly those in the Apple and Google stores, are created and marketed by individuals and small businesses. In fact, independent developers made $20 billion in the App Store in 2016 alone.