This is a Plasma 5 applet that acts as a separator between applets. This plasmoid is coming from Latte land but it can also support Plasma panels.
Latte Separators between window icon, title and application menu
Appearance Settings
- Plasma >= 5.8
This is a QML applet and as such it can be easily installed from Plasma 5 Widgets Explorer or alternative you can execute plasmapkg2 -i . in the root directory of the applet.