There are numerous printing companies that will print your designs onto not just T-shirts, but also hoodies, hats, posters, cushions, bags, and phone cases, to name a few items. These businesses also offer fulfillment services. This means that you promote the merchandise on your own site and once you sell a product the printing company will not only print your design but also send the item directly to the buyer. So all you have to do is concentrate on the marketing and selling of your products, and the fulfillment company will take care of the rest.
It works essentially the same way as the phone apps do above. If you don’t care to let Google know what you do on a daily basis, you can make money from home by letting them monitor your Internet usage. They use the information they gather to help them market/increase the functionality of their advertising programs when targeting users that are similar to you.
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.