Code Avengers (www.codeavengers.com)

Code School (www.codeschool.com)

Tree House (www.teamtreehouse.com)

Udacity (www.udacity.com)

Code HS (www.codehs.com)

Khan Academy (www.khanacademy.org)

SQL Zoo (www.sqlzoo.net)

Here,I describe the full details of above mentioned sites.

The website code academy offers HTML,PHP,PYTHON,API,RUBY,JS,JQUERY  at free of cost.

code avengers offers HTML5,CSS3,JAVASCRIPT at free of cost.