I built https://www.stoodious.app for my wife while she was studying for her California Real Estate Broker's Exam. She was frustrated with the price gouging on text books, or being the "state-of-the-art" study platforms being video only, having no/poor mobile UX or just feeling outright dated.

So I built Stoodious as a study guide platform that intends to give you the material and get out of your way, as opposed to the engagement-driving gamification of others. One of the killer features is being able to drill practice questions related to the specific study section you're working on - e.g. 20-30 questions about water rights, encumbrances or calculating GRM. Frequently my wife found herself studying vocab for a section but having to skim through a 100-question practice test to find related questions.

I extended the material to all 50 states' basic real estate licensing exam and am looking to add even more "professional exam" material.

If you want to expand into other areas, it might be worth adding Amateur Radio (HAM) License training materials as a next step. Relatively well defined, also an area of technology that deserves more attention.