AtlasOS, formerly DucKOS is a online web-based operating system written mostly with Java and HTML. Proxy backend from Ultraviolet
App store is coming soon, and put some app suggestions in Issues
You can host the website by yourself, with your own domain that you can register from freenom.com, by cloning this repository and linking it to your Netlify account. Further instructions won't be neccessary since it will be on Netlify