Duolingo es un sitio web destinado al aprendizaje gratuito de idiomas a la vez que una plataforma crowdsourcing de traducción de textos. El servicio está diseñado de tal forma que a medida que el usuario avanza en su aprendizaje ayuda a traducir páginas web y otros documentos. 

Actualmente el sitio ofrece cursos, desde español, de inglés, francés, alemán y portugués, italiano o neerlandés (desde inglés), aunque nuevos cursos de idiomas están en proceso de creación gracias a "La incubadora de idiomas". 

ozdic - the English Collocations Dictionary online

www.ozdic.com brings you a completely new type of dictionary that will help English lerners write and speak natural-sounding English. Collocations - common word combinations such as 'bright idea' or 'talk freely' - are the essential building blocks of natural-sounding English. The dictionary contains over 150,000 collocations for nearly 9,000 headwords.The dictionary shows all the words that are commonly used in combination with each headword: nouns, verbs, adjectives, adverbs, and prepositions as well as common phrases.The dictionary is based on the 100 million word British National Corpus. Internet searches were made to ensure the most up-to-date usage for fast changing areas of language such as computing.Over 50,000 examples show how the collocations are used in context, with grammar and register information where helpful.The clear page layout groups collocations according to part of speech and meaning, and helps users pinpoint speedily the headword, sense and collocation they need.Usage notes show collocations shared by sets of words such as languages and seasons.Natural word combinations and alternative expressionsAcademic and professional writingIdeal for IELTS, TOELF