If you are into Web 2.0, then you probably know about Ruby, one of the most preferred Web 2.0 programming languages. And here is a free e-book introducing you to Ruby: Mr. Neighborly's Humble Little Ruby Book (http://www.humblelittlerubybook.com/book/)

You can download the e-book as a PDF or view it online.

Found via Lifehacker (http://www.lifehacker.com/software/ruby/free-ebook-teaches-ruby-programming-225976.php).

Ruby on Rails is a great framework for developping quickly web apps, that's what we're using for FeedBooks.
Now that we almost support all of the formatting stuff needed for these kind of books, we may start adding tech books too, this way it'll be easy to carry them around with you on your e-ink device (you'll see how usefull a table of content is in this case).

Missed this one on Lifehacker. Thanks for pointing it out!