A new version with some major fixes and improvements is available on the Unity Forum. This version will be deprecated when the new one releases.
Link & Sync is a tool for importing external assets and easily synchronising changes when they occur.
Browse or drag and drop to set a source folder outside your Unity project and a destination folder inside it, then click Sync. It's as simple as that.
This is Link & Sync Pro.
You can try out Link & Sync Lite for free here.
Take a look at the screenshot to see the feature list and comparison between the different versions.
Disclaimer: while every effort has been made to ensure that this system is as intuitive and bug-free as possible, you should always backup your projects regularly (even without this plugin). Kybernetik cannot be held responsible for any loss of data.