xlsx.hwp was written by Andreas Falkenhahn. This plugin was first designed as a proof-of-concept for Hollywood 9's new serialization interface and was later expanded into a full library for dealing with XLSX documents. Thanks have to go to Kenneth Troldal Balslev for his wonderful OpenXLSX on which this plugin is based.
If you want to contact me, you can either send an e-mail to andreas@airsoftsoftwair.de or use the contact form on http://www.hollywood-mal.com.