WP-Filebase Pro can put all files of a category (and its sub-categories) into a single ZIP files. Users can download whole categories without clicking trough all their files.
To provide the link to the ZIP file use %cat_zip_file% in your category template. If you want to insert the links somehwere without using a file list, do it like this (replace 123 with the category ID):
<a href="http://example.tld/?wpfb_zip_cat=123">Download ZIP</a>