PushOwl Web Push Notifications is the more common of the two in our index: it runs on 18 websites against 7 for CartStack. Counts come from real scans, not vendor claims.
CartStack is a SaaS solution that allows any company with an ecommerce site or reservation system to increase revenue through reminding/encouraging consumers to return to their abandoned cart and complete their purchase.
PushOwl Web Push Notifications are a Shopify app which helps recover abandoned carts and market better with web push.
Want to know which one a particular site uses? Look it up and see its whole stack, or compare two sites side by side.