Using this site you can check your understanding of the key points of Japanese grammar by reading explanations of each with example sentences.
- As well as English, explanations of the fundamental grammar points are given in 12 different languages.
- The site is currently undergoing a re-shuffle, and it seems that the author is aiming to create a more complete guide to the study of Japanese.
- There is a grammar guide.
How to...
Here's the contents page of the grammar guide. There is a list of key points arranged by level, from beginner to intermediate to advanced.

This is the list of languages other than English which are supported.

We selected 'Italian'.
It appears that not all the grammar points covered in the English version are translated into Italian, but most of them are, making it very convenient for Italian speakers not so confident in English. The multilingual support makes this site really useful for learners, don't you think?
In the blog, there are detailed information on Japanese, so you can find a lot of it just by reading the blog of the site.
This site is also introduced in an "e! Kore" article called Start learning Japanese from zero. If you're interested, please take a look!