ZeroPayInstalment_Basic demonstrates the functionality in basic HTML should a customer work off a customised platform, or if you need to create a version of this for a platform we don't currently support.
ZeroPayInstalment_Shopify is the plugin developed as a theme extension for an existing Shopify plugin.
ZeroPayInstalment_Wordpress and ZeroPayInstalment_Magento are the plugins developed for Woocommerce and Magento respectively.