Not long ago I was working on an integration between WooCommerce and some payment gateway. WooCommerce is an e-commerce solution in a form of a WordPress plugin. It extends your WP website to provide you with an online store, and it is a widely-known and recognized solution.
I needed to develop something very simple that required me to save some additional data about orders that used a certain payment gateway for checkout. I was surprised when I failed to find a functionality in WooCommerce core that would enable me to do this. Naturally, I wrote a plugin.