prism.js - Prism is a lightweight, extensible syntax highlighter, built with modern web standards in mind.
highlight.js - Highlight.js is a syntax highlighter written in JavaScript. It works in the browser as well as on the server.
Bright - React Server Component for syntax highlighting.
Rainbow (Syntax Highlighting) - Simple syntax highlighting library written in JavaScript.
code-ray - Live debugging tool for software developers
Pygments - Generic syntax highlighter suitable for use in code hosting, forums, wikis or other applications...