What are the top Bikeshed repos?

Popular Bikeshed repositories on GitHub, each answered in plain English for non-coders: what it is, its tech stack, and how to run it.

w3c/serviceworkerThe official W3C specification document for service workers, the browser technology behind offline web apps, w
w3c/intersectionobserverThe official W3C specification for Intersection Observer, a browser API that lets a page detect when an elemen