The simplest "open folder in system file manager" plugin I could create.
There are a few of these things around, but they are more complicated than we need.
Given the increased pace of NetBeans and Java releases I want something that is easy for me to keep running on the latest version of NetBeans.
Tools > Plugins > Downloaded > Add Plugins...
Right click a folder in the project pane, then select Open in File Manager
. This will work on project roots, and packages in the Projects pane, and any folder in the Files pane.