Shopify Flow is one of the most powerful apps on the market, and it's completely FREE! What makes it so powerful is that you can use it to automate "if this then that" type of tasks. Things like "assign products to a collection" or "add tags to a customer", here are a few pre-built Flows that we find useful (you can download the flow and use the Import feature of Shopify Flow to import the flow into your Shopify instance).
Download Shopify Flow from the Shopify App Store
Current Flows that are documented (with downloadable Flow Example):
Some Flows we are working on documenting:
Tag comics with storylines (Absolute, Ultimate, One World Under Doom)
Add to Subs order tag for people who add items to their subscriptions a website
Add/Remove new release tag for products
Stock Level based:
Daily- publish and unpublish products based on inventory levels.
Email based:
Encourage customers to subscribe after first purchase email flow
Send customers a satisfaction survey after order is received.