Stamped.io is a tool to collect customer reviews. It's got nifty features including the ability to capture review feedback directly inside email, or the ability to request reviews via Facebook Messenger. Easily leverage the reviews you've gathered by displaying them on your product pages.
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.
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.