Top Alternatives to Semantic UI

Bootstrap is the leading open-source HTML, CSS, and JavaScript framework for building responsive, mobile-first websites and web applications quickly and efficiently. It provides a vast collection of pre-built components and utilities.

Foundation is a comprehensive family of responsive front-end frameworks designed to streamline the creation of aesthetically pleasing and highly adaptable websites, applications, and emails that maintain their visual integrity across all devices.

UIKit is a comprehensive, modular, and lightweight front-end framework designed for building fast, responsive, and powerful web interfaces across various devices and screen sizes.

Materialize is a modern, responsive front-end CSS framework based on Google's Material Design principles. It offers a collection of ready-to-use components and styles to build visually appealing and highly functional websites and web applications quickly.

Skeleton is a minimalist boilerplate for responsive development. It provides essential CSS styles and a simple grid system to kickstart adaptive projects without the bloat of larger frameworks. Ideal for smaller projects or developers who prefer building upon a clean foundation.

W2UI is a lightweight JavaScript UI library offering a comprehensive collection of standard web widgets like grids, toolbars, tabs, and forms, designed for building desktop-like web applications with minimal dependencies.

Bulma is a modern, open-source CSS framework based on Flexbox. It provides a collection of pre-designed components and a responsive grid system to streamline front-end development and build elegant web interfaces quickly.