This might be too advanced for most of us, me included, but for anyone interested here it goes:
I use it for English and French and it's completely free. Apparently they ran a fund-raising in 2010 and 2013 and that's where they got their money for the project.
There's only 127 books in Japanese, though. While there's 40354 books in English haha As per usual…
by PolyglotPaul