What are the free online programming training services?

Question

ruby

Not so long ago I came across the site www.lynda.com. All materials are of very high quality, the only negative is that almost everything is not available with a free account. Maybe someone knows a free analogue or any other service where there is something to read on various programming languages ​​/ frameworks, etc.
Thanks for any links and advice.
PS In order not to produce questions, I immediately want to ask the second one - has anyone met a resource / book on the Chrome API (extensions & apps)? I would like to find some quick source of information that you can always keep at hand (although the official documentation is good, but for me - everything is too scattered).

Answer 1

coursera.org
udacity.com
codecademy.com

Answer 2

Post from habr .
Post from lifehacker .
Almost everything has been collected (on Habré, in the comments, everything that is not in the article was added).

Answer 3

codecademy.com
codeschool.com
rubymonk.com
iwanttolearnruby.com - list of courses