Below is the list of Shopify Apps and the key purpose they solve that are recommended to be installed if your website is on Shopify- 

Key Purpose
Shopify App NamesAbout the App
MarketingAdYogi ProIncrease your sales by automating ads for your eCommerce store

AdYogi Retargeting AppA well-devised app to automatically retarget your visitors  
Push Notifications Izooto Marketing platform to help you build your audience and keep it engaged via Web Push Notifications 

Push Owl Web Push NotificationsAn app to convert your one-time visitors into loyal customers with push notifications 
Search SolutionSearchTapSaaS-based search technology product that helps improve user engagement and search-led conversions 
Cart Recovery SMS Notification Cart RecoverySend SMS alerts to abandoned carts
Logistics VamashipHelps in making E-commerce shipping easy and cheap with realtime delivery tracking

ShiprocketLogistics software which offers automated shipping solution
Shipment TrackingShipway - Shipment TrackingAn all in one shipment and package tracking tool & tracking APIs for eCommerce 

Whatsapp Chat + Cart RecoveryProvide quick & easy customer support service via Whatsapp chat button 
Invoicing Invoice FalconThis app automatically sends a PDF invoice of the order to your customer 

GST Invoice IndiaAllows you to generate GST ready invoices 
Reducing RTOsAdvance Cash on Delivery - Shopify app to limit COD on certain pincodesControl how buyers use COD on your store 

Thirdwatch (by Razorpay)An AI-driven solution that helps online sellers prevent Return to Origin (RTO) 

COD Order ConfirmationAuto order confirmation via phone call & SMS for Cash on Delivery orders. 
Payment GatewayRazorpayAll in One- Payment gateway