Stylify CSS is a library that uses CSS-like selectors to generate optimized Utility-First CSS dynamically based on what you write. It also allows you to define components, variables and global selectors.

NumVerify offers a full-featured yet simple RESTful JSON API for national and international phone number validation and information lookup for a total of 232 countries around the world.

Simple tooltips made of pure CSS and made by Claudio Holanda. Balloon.css lets you add tooltips to elements without JavaScript and in just a few lines of CSS.