Amara (formerly Universal Subtitles or unisubs) gives individuals, communities, and larger organizations the power to overcome accessibility and language barriers for online video. The tools are free and open source and make the work of subtitling and translating video simpler...
It's called collaborative translation. To make it simple, people help each other translate interesting foreign language texts into their native language. It's mostly blog posts, magazine articles, short stories and another materials licensed for free redistribution.
The official website button opens an empty page (as of January 2015)