WhatWeb

whatweb <url>

Tool for identifying web technologies (CMS, frameworks, servers, libraries) used by a site.

During active reconnaissance phase, to know what technologies a website runs before launching specific attacks. WhatWeb tells you if it's WordPress, Joomla, Apache, Nginx, PHP, etc. This allows you to plan attacks targeting specific versions.

If the site uses Cloudflare or a WAF that hides the fingerprint, WhatWeb may give limited results. Also if you only need a lighter tool, like Wappalyzer in the browser.