The Rosetta Stone is an ancient stela which was found in the city called Rosetta, Egypt in 1799.

At British Museum
There are written the same sentence in three ancient languages. Hence, it uses as a metaphor for decipher, translate, complicated question and significant key.
Now, It is also famous name for learning foreign language programs.

I've got a Chinese
They launched to Japan a few years ago and expanded its business quickly.I had been browsing their website for a couple months and finally I've got them.I think it well combines with the way of Japanese people study which usually focus on Reading and Writing not Speak or Listening. Let's see how it works.
Comments
I'll tell you more about it when I complete it.
My opinion so far, if you really wish to master a foreign language, RS is yet deficient. It's the best and much reasonable to have a good-quality grammar book.
(It works for me.)
However RS gives you a motivation to continue study which is a principle to learn a foreign language.
Endurance makes you stronger!