CSS frameworks are in constant state of evolution and improvements. They are quite popular and used these days. I have listed some of the most popular.

1. Bootstrap framework

Bootstrap is a free and open-source front-end web framework for designing websites and web applications. It contains HTML- and CSS-based design templates for typography, forms, buttons, navigation and other interface components, as well as optional JavaScript extensions. Unlike many web frameworks, it concerns itself with front-end development only. Ther are two version for now. Stable version 3.3.7 and preview version v4.0.0-alpha.6. 

2. Foundation framework

Foundation is a responsive front-end framework. Foundation provides a responsive grid and HTML and CSS UI components, templates, and code snippets, including typography, forms, buttons, navigation and other interface elements, as well as optional functionality provided by JavaScript extensions. Foundation is maintained by ZURB and is an open source project. Current version of fondation framework is 6.4.3.

3. UIKit framework

UIkit is a lightweight and modular front-end framework for developing fast and powerful web interfaces. UIkit gives you a comprehensive collection of HTML, CSS, and JS components which is simple to use, easy to customize and extendable. There are two version in use for now, v2, and v3 version.

4. Materialize framework

Materialize is a Responsive CSS Framework based on Google’s Material Design Language. Materialize provides a responsive grid and HTML and CSS UI components, templates, and code snippets, including typography, forms, buttons, navigation and other interface elements, as well as optional functionality provided by JavaScript extensions.

5. Bulma framework

Bulma is a free and open source CSS framework based on Flexbox. Bulma appears to be a fairly new addition to the suite of modern CSS frameworks. From first glance the base library looks clean and fresh. It provides a modular sass framework to optimize your bundle to only the necessary classes which we will use as much as possible.

There are many others css frameworks like Pure.css, Kube, Vuetify, Zap, Framy, Tailwind, mini, etc.

In the following articles I will explain some of them in detail.