This replaces your standard custom post meta form. Allows extension of page, post and custom post type by allowing you to create customised post form fields when adding or editing post types.
This is typically for developers to extend your typical post and post type form. You can use get_post_meta function in your theme template to display the saved data.

WP Extra Fields

Allows extension of page, post and custom post type by allowing you to create customised form fields to include when adding or editing post types.

Andrew Norcross

tripflex

Creates a panel to change or delete meta keys in bulk. Useful for when you are switching plugins or themes that use specific meta keys for functionality, or for general cleanup for older sites that may have older meta data that is no longer in use.

Post Meta Manager

A simple utility plugin for changing or deleting post or user meta (custom fields) keys in bulk.

WP Extra Fields vs Post Meta Manager