Assets on Unity Asset Store

90's Desktop OS UI - UI pack that looks of 90's desktop operating systems
View on Unity Asset Store
Documentation PDF

3D Interactive Knobs, Sliders and Buttons - Asset package for adding in-world controls
View on Unity Asset Store
Unity forum post
Documentation PDF

Open source assets

Prefab Menu Tool - Editor tool that allows you to add your own prefabs to the GameObject menu
Source on Github

OatsUtil - Collection of methods and extensions for Unity components, C# collections and numeric operations
Download package
Source on Github

Screenshot Utility - Tool for taking screenshots and other features to help take screenshots
Download package
Source on Github

Object tub - Simple object pooling with easy to use API
Download package
Source on Github