Even though Practicing Ruby is a paid service, a good portion of its content has been released under a free documentation license. You can find the archives for the first four volumes (over 60 articles) below:

• Volume 1
• Volume 2
• Volume 3
• Volume 4

I wrote the first three volumes by myself, but the fourth volume features guest articles by James Edward Gray II, Piotr Szotkowski, Avdi Grimm, and Greg Moeck.

I hope you enjoy these articles, and if you do, please spread the word and consider subscribing to Practicing Ruby to support its ongoing work. This is still mostly how I pay my bills, so any help I can get is appreciated!