* Generates real revenue (either subscription, or one-time)
* Regularly used (e.g. a few dozen people who log on every other day)
* Useful enough that its users would be sorely disappointed if you pulled it
* Recommended openly on the internet (e.g. Twitter, Reddit) from people who have no relation to you
My advice: don’t boil the ocean, show you can have really high quality craft. Be playful and engaging. Show the meta work. Have good git hygiene. Write a blog post about why you refactored something and ask for public code review. Show from afar that you’d be great to work with.
One example is a Chrome extension I made when I was in college that enhanced my alma mater's course registration page. I didn't have any entrepreneurial skills at all, but quite a few people were disappointed when it was later shut down.