grammatical number - Should the noun after "any" be singular or plural?

I always thought with "any" I should use the plural, but on the internet I can find both:

• It can be found in any book.




• It can be found in any books




• Do you have any books?





• It can be said in any language.




• This can be understood by anyone.




• It has been used in any form.

So, what's correct?
Is there any rule?