Hbdl is a scraper – a tool for the automated downloading of books from HebrewBooks.org. From the README:
Hbdl is an tool for automatically downloading books from HebrewBooks.org. It has two modes: ‘update’ and ‘range’. The default is ‘update’, in which the program tries to download books listed on HebrewBooks.org update pages …
If a ‘r’ / ‘range’ argument is given, then the program will run in ‘range’ mode, and simply try to download the books whose numbers are within the given range.
Please note that Hbdl is a scraper, and as such, it is quite fragile, containing hardcoded assumptions about the structures of URLs used by HebrewBooks.org and the contents of HTML / XML served by the site. If these change, the program will have to be rewritten.
Hbdl is implemented in Perl, and is available under the Artistic License.
Hbdl has been developed and tested on Debian GNU/Linux, but it should work on any *nix system. It does not, as far as I know, use any OS-specific code, so it may work on other, inferior operating systems, as long as they have a Perl environment.
Update II: I have been asked to cease making Hbdl available for download; I have complied.