Use Twitter + API for something. I have used it before, and it is quite the nice information source.
Make a screen magnifier. Many exist, but I want to make one myself.
Learn how to judge strings as being "similar" and make some sort of fuzzy search.
Make a basic game. Then add local co-op. Then add online co-op. Then add a chat.
Make a pretend stock simulator. Get actual stock prices from
the internet. Give user choice to buy and sell stocks, and have
the ability to bring up how much the user made. Have a history
with user's purchases and profits. Store data in SQLite.
Prerequisites: Learn how stocks actually work.
Also attempt to tack on some machine learning to the stock
simulator to try to help you predict when and what to buy and
sell. Initial research suggests that this will be pretty much
impossible and doomed to fail.
Prerequisites: Learn how to make machine learning models, better statistics knowledge.
My parents own a hotel, so make them something to manage customers, employees, finances, and reservations with. Definitely give it a nice GUI. It would be important to learn security practices or just not to include desirable information like credit card information.