Interesting article on the Mises blog:

The English Wikipedia alone includes nearly two million articles, and has a word-length fifteen times that of the Encyclopedia Britannica. Wikipedia is the single largest encyclopedia ever assembled, having long since surpassed the Yongle Encyclopedia of 15th century China.

The man credited with founding Wikipedia, Jimmy Wales — known to Wikipedians as "Jimbo" — was a finance major at Auburn University when the Mises Institute's Mark Thornton suggested he read "The Use of Knowledge in Society," a now-famous essay written by Austro-libertarian economist and Nobel laureate Friedrich von Hayek. ... According to a June 2007 Reason magazine interview, this insight of Hayek's is what led Wales to found Wikipedia. The rather lofty vision that inspired Wales? "Imagine a world in which every single person on the planet is given free access to the sum of all human knowledge. That's what we're doing."

Those who refused to believe that a user-generated encyclopedia could compete with the monolithic, traditional encyclopedia written by experts and organized by professional editors, were no doubt shocked when Nature magazine published a 2006 article comparing Wikipedia to the well-known Encyclopedia Britannica. The article concluded that Wikipedia articles were comparable in accuracy and thoroughness to those of the older, paper encyclopedia.

According to [a Pew Research Center] study, "Wikipedia has become the No. 1 external site visited after Google's search page, receiving over half of its traffic from the search engine." All that traffic does not include sites that syndicate Wikipedia content, such as Ask.com.

Such syndication is free thanks to the special license agreement to which all contributors consent when adding content to the encyclopedia. The GNU Free Documentation License (GFDL) allows for royalty-free reproduction — in original or modified form — even in for-profit projects.

I have an attraction to GNU projects: I've been using GRETL (Gnu Regression, Econometrics and Time-series Library) for both instruction and research. I co-authored a review article that describes GRETL's capabilities as of a couple of years ago. As happens with things GNU, these have increased a good bit since then.