Massive-scale online collaboration and its application

Do you know Captchas? These awful and most of the times somewhat unreadable combinations of numbers and/or letters you are asked to enter on some web sites in order to verify that you are actually a human being and not a robot or malware program? If the answer to that question is "yes", then you might also have been struck by the thought that every time you enter these characters a small part of your valuable life time is just wasted. But it is not. 
Did you know, that you are actually helping to digitize books and other content by entering these captchas? Through massive scale online cooperation we are all contributing a little bit to the digitization of human knowledge. Also, by using the free online language learning web site Duolingo people are not just improving their abilities in speaking a foreign language but they are also helping to translate web content (e.g. Wikipedia articles) from one language to another supporting the sharing of knowledge across language boundaries. Awesome!

If you are interested I suggest you watch this very inspiring TED talk about this topic here: 

Luis von Ahn: Massive-scale online collaboration