GemPages is one of the most popular Shopify apps for designing web pages. It features a library of templates you can choose from: you can filter them by type (landing page, product page, blog post, etc.) or search by keywords (there are templates for special occasions or specific types of products).
Besides tailoring a chosen template to your needs, you can create pages from scratch by adding blocks and elements from GemPages drag-and-drop editor.
The app tries to adjust to your needs and asks you several questions before you try out the editor. Based on your answers, GemPages will suggest the most suitable templates and page building tips.

The GemPages app is nicely integrated into your store. Even when you create pages using a default Shopify editor, you can customize those pages with GemPages:

Unfortunately, there’s no free plan offered. There are three monthly subscription types, each with a 10-day free trial: Starter ($15), Business ($29), and Advanced ($59). The Starter plan is limited to 2 page types and has a limit on all elements and integrations. Other plans include unlimited templates and design components, while Advanced differs in having page scheduling and priority support.
There’s also a possibility to discuss discounted pricing if you want to use GemPages on several Shopify stores.