Yet another Amazon service providing the possibility to make money online is the Audiobook Creation Exchange. You can create a standalone audiobook, or create an audio version of your eBook as complementary media. And you can narrate your audiobook yourself, or Amazon can put you in contact with a professional to help. Once sold, you can then earn up to 40% royalties per audiobook.
If you have a good idea for an app, and the skills to create it, then producing your own premium app can be profitable. However, with so many free apps available, it may be hard to convince people to pay. If you want to go down the premium app route, consider having a basic free version to encourage people to download the app in the first place. You can then provide the option of upgrading to a premium plan once users realize how useful the app is.