Jimmy Wales, Larry Sanger, 2001

In 2001 Jimmy Wales and Larry Sanger launched Wikipedia: a free online encyclopedia. What is unique about Wikipedia is that all the articles are open content; anyone can edit any article at any time. Every day about 100,000 volunteers help out to correct the spelling and grammar, check facts and sources, lay out articles and report vandalism and other fraudulent behavior. Wikipedia has collected more than 4,000,000 articles in English and over 19,000,000 more in over 285 languages. If the total content of Wikipedia were to be published in book form, you would need a bookshelf that can hold 5,542 volumes.