Touch Translate is a tool developed for language learning.
The idea is that you download a copy of familiar book in the language you wish to learn and attempt to read it, but with the assistance of being able to touch on any word to get the literal translation of that word. It's surprising how quickly you pick up words and sentence structure of the new language this way.
Built on node - uses google translate api, a custom express mini api and a socket.io go-between server and client. It's optimised (I use that word very loosely) for mobile.