wget

Wget is a network utility to retrieve files from the web using HTTP(S) and FTP, the two most widely used internet protocols. It works non-interactively, so it will work in the background, after having logged off. The program supports recursive retrieval of web-authoring pages as well as FTP sites – you can use Wget to make mirrors of archives and home pages or to travel the web like a WWW robot.

Only use this tool against systems you own or are explicitly authorized to test — see the disclaimer.