Here is the concept in a nutshell. Start with WP. Install ACF Pro and/or ACF Engine Pro (which contains ACF Pro embedded into it). Install a minimalist theme built for block-based rendering such as Blocksy. You now have your application development platform ready. Let the no-code configuration of your content structure begin. Use ACF Engine to define post types, taxonomies, option pages, and of course, do the all the important rendering using ACF Engine’s rendering features. This includes templates, loops, single pages, custom queries, internal block types and the capability to make your own custom block types as needed for your project.
Here is the key point we’ll make about using WP as a rapid development framework for applications. It is probably best to take the approach (using multi-site networks or pre-configuration of stand-alone WP installs) of 1 user equals 1 WP site. In other words rather than trying to cram all users into 1 WP site, which tends to feel a bit messy when we’re thinking in terms of the way data is stored in posts and post meta, instead we’re looking at a nice (luxurious even) space for each of the apps users.
The process of making an application structure with ACF Engine is quite similar and consistent regardless of what specifically you are building. There are some features you might need for some projects and not for others, but the basic workflow and design system is universal.
Start with a custom post type, add any taxonomy(s) that you need to go with it. Then add field groups for the post type and/or taxonomy(s). Already you have a functional system for storing your data, and all the versatility you could want as you are not locked into either the settings for your objects (post types, taxonomies) or the associated field groups. Everything can still be modified with a few clicks.