wget and cURL come into mind, although I'm not sure if either of them can copy an entire site. Remember that (security vulnerabilities aside) you should never be able to download the code behind the site (like the PHP which is run before the site is served to you) or the raw contents of the database, so things like search boxes, most logins, etc won't work even if you manually downloaded every single file. Thus you can't save Google and get the entire internets 😉