Payment gateway software is usually delivered pre-integrated as part of an e-commerce platform. This type of software can also be used separately by companies who do not want to limit their options to the integrations provided by e-commerce vendors. While most providers of e-commerce platforms offer integration with the most popular payment gateways, other options may be preferable, especially for markets that aren't well served by the main players.
One important thing to point out is to not get overly excited with WooCommerce’s seemingly attractive pricing too much. While, yes, the platform itself is free, and all the components needed to make it operational (including PayPal payments, etc.) are free, you might need a number of paid extensions to get some helpful additional features. This will grow your bill.
Oracle Commerce is the industry's top-ranked commerce solution that powers the world's best brands, and delivers a consistent, personalized cross-channel customer experience. Oracle Commerce offers a complete commerce software platform that enables you to deliver a personalized customer buying experience across all customer touchpoints, including the web, contact center, mobile devices, social media, physical stores, and more.