w3schools

http://w3schools.com/

Subjects:

HTML Tutorials

Learn HTML
Learn HTML5
Learn CSS
Learn CSS3
Learn TCP/IP

Browser Scripting

Learn JavaScript
Learn HTML DOM
Learn DHTML
Learn VBScript
Learn AJAX
Learn jQuery
Learn JSON

XML Tutorials

Learn XML
Learn DTD
Learn XML DOM
Learn XSLT
Learn XPath
Learn XQuery
Learn XLink
Learn XPointer
Learn Schema
Learn XSL-FO
Learn SVG

Server Scripting

Learn SQL
Learn ASP
Learn ADO
Learn PHP
Learn ASP.NET
Learn Razor
Learn .NET Mobile

Web Services

Learn Web Services
Learn WSDL
Learn SOAP
Learn RSS
Learn RDF

Web Building

Web Building
Web Browsers
Web Certification
Web Hosting
Web W3C
Web Quality
Web Semantic

Features:
- Quizzes
- Articles
- Tutorials
- Editor, see browser results