W3Schools.com

W3Schools offers free online tutorials, references and exercises covering web development and programming languages including HTML, CSS, JavaScript, Python, SQL, Java, C, C++, C#, PHP, React, MySQL, Bootstrap, Node.js, TypeScript, Django and Vue, among many others. It provides a searchable reference library for tags, keywords and DOM properties, hands-on exercises across each language with progress tracking for signed-in users, and paid certificates across its covered subjects.

The site also offers an iOS and Android app, an Academy section, and a Spaces feature, alongside a Get Certified and Upgrade path for account holders. Its ads.txt file lists 72 ad system lines.