Duolingo is simply the best ever online language learning programme I have ever come across. It is free, provides instant feedback to the learner, has no advertising, and is very engaging. Duolingo comes as a web resource or an app on both IOS and Android.
I have been using the IOS app for a few months to learn Spanish. After several years and numerous programmes I have made only very limited language learning progress and my interest has always waned. This hasn't been the case with Duolingo; I am hoping to be a competent speaker of Spanish by the end of the year through using Duolingo.
The only limitation is the small range of languages that are available: Spanish; French; German; Portuguese and Italian. However, don't let this stop you. In regards to Spanish, the British Ministry of Education, after extensive research and analysis, selected it as the most worthwhile language for students to learn.