Craft 3 plugins for better author experience
Annotated Notes: For admin notes with automatic timestamps.
Control Panel Body Classes: Add body classes to various Control Panel screens for easier styling (in combination with Control Panel CSS).
Control Panel CSS: To make style tweaks to the control panel. See web/cp.css for styles.
Control Panel Nav: Custom navigation menus for each user type, for easier navigation.
Entry Instructions: Static instruction fields for the CP.
Environment Label: Shows which environment you're in, to help authors only enter content in staging.
Expanded Singles: Remove "Singles" grouping from Entries Index sidebar.
Field Labels: I consider this developer experience, since my alternative is having more fields with specific labels/instructions, but including it just in case.
Help Links: Create a dashboard widget with custom links.
Linkit: Makes it easier for authors to add different types of links.
Readability (on probation): Text statistics to help write more readable text (haven't really tried yet).
Sidebar entry types: Add entry types under their corresponding sections in the Entries Index sidebar.
Tags: See and manage all tags in one place.