W3Schools is an educational website for learning web technologies online. Content includes tutorials and references relating to HTML, CSS, JavaScript, JSON, PHP, Python, AngularJS, React.js, SQL, Bootstrap, Sass, Node.js, jQuery, XQuery, AJAX, XML, Raspberry Pi, C++, C# and Java.
Codecademy is an online interactive platform that offers free coding classes in 12 different programming languages including Python, Java, JavaScript, Ruby, SQL, C++, Swift, and Sass, as well as markup languages HTML and CSS.
IEEE is a professional association for electronic engineering and electrical engineering. Their website is invaluable when searching for standards and guidelines.