https://github.com/sjardim/processwire-simple-flickr-album

http://www.webinfopedia.com/multiple-file-download-by-creating-zip-file-in-PHP.html

http://stackoverflow.com/questions/1754352/download-multiple-files-as-zip-in-php

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jquery

https://github.com/biesiad/jquery-multidownload

** $('.my_download_trigger').multiDownload({ delay: 500 });
http://stackoverflow.com/questions/9047645/download-multiple-files-without-using-zip-file

https://github.com/sindresorhus/multi-download