Shopify is a commerce platform that allows anyone to set up an online store and sell their products. It's the go-to eCommerce platform for young direct-to-consumer brands. It's ease of use and setup is what's most attractive to merchants, but also the incredibly vast Shopify app store.
Klaviyo is the best in class email marketing solution for eCommerce. It's powerful because it connects to your store, and you can create awesome customer segments based on past purchasing behaviors, customer preferences, and even future predictions of spending.
Webflow commerce is becoming a serious competitor to Shopify. They also boast the ability to create a fully functioning website without touching code, but in addition to that - they pride themselves on giving you the ability to create unique commerce experiences for your customers.