I'm searching a stand-alone script, which works simlar as the
"Customers who have bought this product, also purchased" feature on
amazon, but for a content site like "Users who have viewed this page
also visited". The script should show only internal links, e.g. for
each page the most relevant page titles incl. their links to other
pages of the same website.

Requirements:

- The script must be free to use / Open Source (also for commercial use).
- The script must be easily to install even for someone who is not a programmer.
- The script must be easily to include in the website and to adapt the page layout.
- It must be a stand-alone script, not a complete shop or CMS solutions.
- The script must be written in php or eventually perl.

Can someone suggest where to get such a script or doesn't exist something like this?

I think there's no such stand-alone script.

1984 is the book where scripts like this could have existed. Maybe
when Homeland Security gets their hands on Google search logs your
magic script will be created. Just replace 'visited' with 'searched on
Google.'