I made hotcold typing - http://hotcoldtyping.com , a touch typing learning tool with instant feedbacks. I released initially as chrome app with free and pro versions. Pro version didn't go anywhere. Since then I changed to 'support developer' version and made the tool free in website also. So far, I had only one buyer for ' support developer' version. But still, I'm proud my work in the app.

I never had any intention to add ads, and always wanted to have a clean, hassle free experience for the learner. Even though, I could make a few bucks from it, I'm not interested in it. It does not have any maintenance costs. Just a static web app hosted on github.

Edit - fixed the web address. was typing from phone :)