Unfortunately, as far as I can see OnLine Grammar Checker is no longer available. Its official website is not functional and you can't even order the application. There is an installer still available on the link above, but it's only a demo version and once it expires you won't be able to purchase an activation key to keep using it.
As far as spellcheckers for the Arabic language go, there are a couple of online services such as SpellChecker.net or SpellCheck.net that could help you out.