ACF

ACF is how serious WordPress builds handle content modelling. Instead of stuffing arbitrary HTML into the default content area, you define the fields each content type needs, and editors fill in those fields rather than a giant text box.

ACF Pro adds Flexible Content (block-style composable layouts), Options pages, and the Repeater field, all of which we use heavily on builds where editors need structured layouts but the project doesn't justify going full block theme.

There's also a Gutenberg block bridge, ACF can register custom blocks via PHP without leaving the ACF workflow. Useful on transitional builds.