I created a Natural Language Processing startup that developed a multilanguage API. We created a frontend for that API with some success. Couple of years before, the startup died. We let the website running for free several years but the server burned in OVH fire in 2021. Then, I create a MVP frontend in react and add ads from adsense. Now it's making $400/month.

I love it because is 100% passive. Improvement ideas are very welcome.

http://linguakit.com