busuu.com is an online language learning community with over 15,000,000 users worldwide (their figures not mine). On busuu.com you have free access to interactive language courses in 12 different languages, including English. You can also interact with other native speakers from the community via an integrated video chat application. For more information watch the introductory video. Just like the website, the busuu.com app requires you to register, after which you have access to a selection of course materials at different levels. For full access you have to pay $4.99 per level.
WHAT I THINK
I tried a few of the activities but can't say I was that impressed. The 'lessons' seem very limited in scope and follow a very traditional format: pre-teaching of key vocabulary using images, spoken dialogue, followed by multiple choice tests. But there are no grammatical explanations, and apart from a few drag-and-drop re-arrange-the-words-to-make-a-sentence exercises, nothing which really exploits the touch screen capabilities of the iPad. Cutting edge it is not. The app doesn't seem to have any of the community features or resources available on the website either, so I'm not really sure why you'd want to pay for full access. Lower-level learners might find some of the free material useful, but that's about it.