Unconventional ideas for a brain training program or a series of books
If you come up with a hook/brand you can apply it to various audiences: like the Chicken Soup for the XYZ series.
1. SuperBrain Word Puzzles for kids
2. SuperBrain Word Puzzles for Teens
3. SuperBrain Word Puzzles for Seniors
4. Follow the pattern above and use mechanical puzzles that you can sell.
5. Follow the pattern above and use "math games"
6. create a long term memory training app that asks you to memorize something (phone number) and have it prompt you to repeat it every few days
7. Have a puzzle of the month club and mail physical puzzles like rings, knots.
8. Learning any skill can train your brain: from drawing to cup stacking to yoga. Have a monthly club where it is something completely different every month: ping pong ball and paddle, notebook and colored pencils, harmonica with instructions
You could even follow the pattern of some other companies where it is a rental: this month you get Rubic's Cubes; next month send them back and get a juggling kit or electronics kit. If you figure out how to do it through Amazon your shipping would be essentially free. You could give people credit for anything they send back to you.
9. Monthly philosophic discussions like Socrates and Plato
A small group of like minded people: could make it a podcast
10. have public contests with leaderboards that expire
Typing, Math puzzles for speed.