Here's one that I actually just started last week! It meets all of the criteria, because I've now made a total of 36 cents on it. A completely negligible amount, but it IS technically bringing in extra cash :-p
I do research engineering for a living, and a huge part of that job is data analysis. I collaborate with laboratory testers to perform experimental studies, then they send me the data and I figure out what it means, and how others can use it to make decisions. Being faster at data analysis both makes me better than my competition, because I can do a more thorough study at lower cost, and happier, because I find digging through thousands of spreadsheets incredibly tedious. So I started writing computer programs to do it for me. It's incredible; I can spend a day writing a program, and 5 minutes analyzing a data set, instead of a month manually doing all of the data analysis.
I've started a side company focused around this as a service. I offer consulting services either teaching people to do this themselves, or writing programs that they can use. With a net revenue of 36 cents so far, clearly I haven't found any clients yet. I also write a blog teaching people the basics of how to do this with ads on the site (There's the 36 cents!), and hope to eventually compile blog posts into books to sell.
Right now my main challenge is traffic. Since the site has existed for less than one month, and I only announced it on Thursday, obviously it isn't getting much traffic yet. So I'm creating more content, experimenting with different ways of getting the word out there, learning about search engine optimization, etc. Exciting times!
Here's a link, in case anybody is curious and wants to check it out:
https://www.1000x-faster.com/blog/