Project Wallace is a set of CSS analyzers that check your complexity, specificity, performance, Design Tokens and much more. And all of that in a single web app.

Micromodal.js is a lightweight, configurable and a11y-enabled modal library written in pure JavaScript

Paged.js is an open-source library to paginate content in the browser. Based on the W3C specifications, it’s a sort of polyfill for Paged Media and Generated Content for Paged Media CSS modules.