Also a language learning service, but italki.com has its own focus on this market. italki is a language social network providing free language learning content. In italki, users can find language partners, post their foreign language questions which can be answered by other users, and join groups for language learning. Now users can not only share the language learning materials they uploaded but also collaborate on creating free language learning textbooks by their own. So italki is building probably the largest Wiki for language learning content!