Wget

GNU Wget, a free tool from 1996 for downloading files from the command line. It comes ready installed on many Linux computers and servers, it can pick up a download where it broke off, and it can follow every link on a site to save a copy of the whole thing.

That makes it the usual choice for keeping copies of websites: someone saving a site to read offline or as a backup, a server script fetching a file every night, or archivists saving sites before they disappear.

Worth knowing: Archive Team, the volunteer group that rescues websites before they shut down (GeoCities in 2009 among them), has long used its own version of Wget to do it, sending much of what it saves to the Internet Archive.