Metro UI CSS is described as 'a set of styles to create a site with an interface similar to Windows 8' and is an app in the Development category. There are more than 25 alternatives to Metro UI CSS for a variety of platforms, including Online / Web-based, Self-Hosted solutions, CSS, Mac and Windows. The best alternative is Bootstrap, which is both free and Open Source. Other great apps like Metro UI CSS are Materialize (Free, Open Source), Purecss (Free, Open Source), Tailwind CSS (Free, Open Source) and Fomantic UI (Free, Open Source).
Shoelace.css is a starter kit and not a framework. Customizable through CSS variables, it doesn’t require Less, Sass, or any preprocessing at all. The minified version is only 35.3KB and much smaller when gzipped.