However, like anything else truly worthwhile, apps require a significant investment of your time or money upfront. If you don't have the skills, then you have to hire someone who can assist you in creating a great app. But first you need to come up with an idea that will sell. Do the proper market research and analytics to come up with the right app.
Are you seeing the possibilities here? Think about what book, or series of books you could write to help people in your field of expertise? You might start with an eBook offered on your own website that covers the basics. Use the eBook as an opportunity to tell people about your more in-depth book on Amazon and finally, follow through with an advanced book offering.