I've been doing some work recently with Craft CMS, and its ecommerce plugin Craft Commerce. Although Craft is still up-and-coming, it's doing quite well. The community is great, and I love working with it. Craft itself is quite extensible, and Commerce is progressing in that aspect. A recent project called for a lot of customization of Commerce, and I ended up creating quite a few plugins to handle third-party integrations.
One such instance was to integrate Amazon Pay as a new payment method in Commerce. This had not been done by anyone else to this point, and more than a few clients/developers had asked if someone knew of an existing solution. After a lot of work, I completed the plugin, and I am making it available for purchase here.