WooCommerce is a widely used open source plugin for WordPress. WooCommerce can be used to sell your products, digital products and/or services in an easy and affordable way. It is without doubt the best and most popular eCommerce plugin for WordPress and is in fact now one of the most popular platforms for ecommerce websites overall.
WooCommerce offers support for inventory management, taxes (for easy calculation of VAT) and variation products that allow you to create a single product listing and with multiple variants/options. Due to the enormous popularity of WooCommerce it is also heavily integrated into many third-party services including the likes of Royal Mail Click & Drop.
Accepting payments is a breeze with integration with many of the leading payment gateways such as PayPal, Stripe, SagePay and many others.
My ecommerce website service includes full design and build of bespoke WordPress website setup as a shopfront (or other), utilizing WooCommerce for all aspects of the eCommerce.