Small Paid Web App

Build one small web app that does a job people already pay for, charge a subscription, and keep it running yourself.

Tool costs: $0 - $20/mo
Ongoing time: 8-15 hours per week while you build it, then a few hours a week to fix it.
Difficulty: High

How it works, step by step

Name one paid job (ChatGPT): Write the job in one sentence, and the jobs the app will refuse. Talk to people who do it now.
Build the smallest page (Claude): Make the page do that job and nothing else. Use sample data before you ask for anyone's real file.
Put it on a host (Vercel): Publish it on the free tier. Say what you store and what you do not.
Add a real price (Lemon Squeezy): Put a checkout on it. The payment company takes a cut. Do not claim a user count you do not have.
Ask the first users (Kit): Email the people who have the problem. Ask them to pay or to say why they will not.

A page that turns a messy bank export into a one-page summary for a freelancer, at $9 a month.

People who will talk to a few users before adding features, and who can leave a bug fix for later without abandoning the app.

Build the smallest page that does the job, on the free host, and ask ten people who already do that job whether they would pay $9.