Extensions are installable packages which give CiviCRM new functionality, and this directory provides a centralized list of extensions which the CiviCRM community has created. This listing displays CiviCRM extensions that work on all Content Management Systems (CMS).
For example if it is installed on a CiviCRM system it will minify crm-menubar.css. If Stripe is installed it will minify stripe css/js.
Requires - CiviCRM 5.x, php 5.6
Credit : the Wikimedia Foundation
The implementation used in this extension is based on https://docs.civicrm.org/dev/en/latest/financial/orderAPI/#transitioning-from-contributiontransact-api-to-order-api