Pure CSS
Only 3.8KB minified and gzipped, but packed with features! Pure CSS has been my lightweight framework of choice for over a year now. Want to see it in action? Check out this tutorial I wrote last year.
Info & download: https://purecss.io/
Beauter
I haven’t yet had the chance to test Beauter in a project, but I can’t wait. This tiny (~4KB compressed) CSS framework not only provides you with tools to speed up front-end development, it provides them in a beautiful and clean manner.
Info & download: http://beauter.outboxcraft.com/
Mini.css
A lightweight (7kb Gzipped) framework for crafting a fast site easily.
Info & download: https://chalarangelo.github.io/mini.css/
Milligram
Milligram provides a minimal setup of styles for a fast and clean starting point. With only 2kb gzipped, this tiny but powerful framework is in the top three of the lightweight framework available.
Info & download: https://milligram.github.io/
Dead Simple Grid
Not really a framework but just a simple grid layout that can be used in every project. 250 bytes of CSS code.
Info & download: https://github.com/mourner/dead-simple-grid
Siimple
Siimple is a minimal CSS framework for flat and clean designs. It’s lightweight but packed with features and looks awesome out of the box.
Info & download: https://siimple.juanes.xyz/
Min
Super lightweight and has the particularity to be compatible with super old browsers like IE 5.5 and Opera 9.
Info & download: http://mincss.com/
Lotus
Super small (1.8kb minified + gzipped) but packed with everything you need: Grid, media queries, forms, and more.
Info & download: http://goatslacker.github.io/lotus.css/
Skeleton
With only 400 lines of code, Skeleton is light as a feather. Yet, it features a grid, typography, forms, media queries… all you need for building a quality site in no time.
Info & download: http://getskeleton.com/
Picnic CSS
With a size of only 3kb when gzipped, Picnic is for sure lightweight, but also has everything you need for creating a great looking, functional website.
Info & download: https://picnicss.com/
Any other lightweight framework you like? Leave a comment below.