After re-purposing a computer challenge-response test so that each human-typed response helps digitise books, Luis von Ahn wondered how else to use small contributions by many on the Internet for the greater good. His ambitious new project, Duolingo, will help millions learn a new language while translating the Web quickly and accurately – all for free. Talk recorded 3 April 2012.

T To comment on this video or anything else you have seen on Future, head over to our Facebook page or message us on Twitter.