Polyglot - a really nice plugin for Chrome that translates random words into a configurable target language. Why? So that you can see new vocabulary from time to time while browsing and thus learn new vocabulary easily. I'm currently trying it with Russian and it's really a nice method - with the few words you have enough context of the sentence to deduce the word. This of course does not practice grammar or declensions and conjugations, but as a little vocabulary boost from time to time very useful.