Advanced Custom Fields Pro (ACF Pro) includes everything in the free version and adds more features. It allows you to create custom fields, assign them to post types, and show them on the admin edit screen. ACF has PHP functions for displaying fields in theme templates, and is well documented.
In addition to the 30 field types that come with the free version, the Pro version adds the Repeater, Flexible Content, Gallery, and Clone fields. With ACF Pro you can also create Admin option pages and use PHP to create Gutenberg blocks.