Does Shopify have its own subscription app?

Yes, Shopify does have it's own subscription app. Shopify has created a functionality, which allows apps, such as Seal Subscriptions to create a subscription app solution on top of Shopify's ecosystem. This means that Seal Subscriptions is directly integrated with Shopify and processes renewals through Shopify's subscription API. Merchants using Seal Subscriptions can keep using the secure Shopify Checkout to accept the initial subscription orders in their shops.