There are 2 repositories under metaboxes topic.
Redux is a simple, truly extensible options framework for WordPress themes and plugins!
A Simple and Lightweight WordPress Option Framework for Themes and Plugins
WP Custom Fields is an options, metabox and customizer framework for WordPress aimed at speeding-up plug-in and theme development.
Create custom fields with simple and easy to use WordPress meta box framework.
A Composer package that provides metabox orchestration for WordPress.
A PHP class that facilitates the creation of custom WordPress metaboxes
A WordPress plugin framework.
A WordPress plugin that adds metabox options framework for other WordPress themes and plugins.
Ζεύς — Olympus Zeus is a framework which allows you to make all your WordPress plugins and themes developments easier and efficient.
WordPress Think Framework is a developer-oriented library that gives you the ability to quickly and easily create incredible websites with WordPress. This is an extensible framework for developing WordPress themes. Based on the WordPress API.
Provides a compatible solution for some personalized themes that require custom meta boxes for WordPress.
Just drop the admin folder into your custom WP theme and include the init.php file from your function.php, and you have access to a full range of admin option fields and metaboxes.
Extending Butterbean, a neat little post meta framework by @justintadlock, with custom Settings and Controls
Display SlideShare thumbs as featured image in Wordpress
Visible metaboxes for the block editor: add some contrast and margins around Gutenberg metaboxes.
WordPress plugin to Logus theme