Duolingo

Duolingo is a free language-learning and crowdsourced text translation platform. The service is designed so that, as users progress through the lessons, they simultaneously help to translate websites and other documents. As of December 2013, Duolingo offers Latin American Spanish, French, German, Brazilian Portuguese and Italian courses for English speakers, as well as American English for Spanish, French, German, Portuguese, Italian, Dutch, Russian, Polish, Turkish, Hungarian, Romanian, Japanese, Hindi and Indonesian speakers.

Input: 

By uploaders/document providers: Documents to be translated into a target language
By students: Candidate translations to documents

Human Computation Elements: 

Duolinguo essentially transforms the human computation involved in language learning into that of document translation, enabling this effort to be directly repurposed

Mediative Elements: 

There is complex and extensive mediation -
Motivate students - by providing a challenge gradient, showing students increasingly difficult tasks as their skill improves; peer support to
Preventing gaming - preventing cheating in various ways
Ensuring high quality translation

Category type: 
Citizen Science Social Machines