Advanced Custom Fields Pro, usually just called ACF Pro, is the plugin developers reach for when WordPress on its own is not enough. The free version lets you add extra fields to posts and pages — a text field, an image, a date — but Pro adds the field types that make it a real site-building tool. The repeater field lets you add the same group of fields as many times as you need, which is how you build things like team member lists, pricing tables and image galleries without a page builder. Flexible content is similar but lets you choose between different layouts for each row, so a page can be built from a stack of blocks. Pro also adds options pages for site-wide settings like a phone number or logo, gallery fields, clone fields, and the ability to turn field groups into Gutenberg blocks. It is aimed at developers and agencies, but the interface is friendly enough that a site owner can add a new field without writing code. If you build custom WordPress sites, this is close to essential.