Three Column Layout Screen
https://wordpress.org/plugins-wp/three-column-screen-layout/
Allows for more modified layout screen for Pages and Posts. Drag and drop metaboxes into 24 different layout options. Makes better use of space on editor screens.
Great example is Music Library. Able to put Composers and Arrangers side by side to make better use of space without having to find or create a custom metabox.