Cafe Press: This website allows you to create digital designs that can then be sold on the platform. You'll earn a commission for everything that sells and you'll never have to deal with printing, warehousing, customer service and so on. The site has over 2 million independent designers that have created products being sold online here. If you have some graphic design skills, then this is a great potential source for your web-based income.
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.