Musculoskeletal pain i.e chronic back and join pain is a huge problem and millions of people have this problem. Here is a solution.

264: Marital and relationship problems solving App

Vijay Peduru provides one million-dollar startup idea every Tuesday. 
These ideas won't help you build the next Instagram or Twitter, but would help you
create a $2K to $10K MRR(Monthly recurring revenue) business. The goal is to help you accumulate half a million to a million dollars in 3-5 years.
These ideas could be easily implemented without much tech background.