requires: gimp from 2.7 (using layer groups)
found: <Image>/Filters/Generic/Split/Frequency separation

The script separates a layer in its high and low frequencies.
This is often used when retouching a portrait, in order to smoothen the skin.
I always forget how to make the low and high frequency layers, so I wrote the script.
It uses the "despeckle" plugin, I thinks, its better than the "gaussian blur" so the slider
reaches up to 30 (the upper value in the despeckle plugin), but feel free to change the
blurring part.
It can create the separation either for the current visible (this is default for any other
similar script, and also the default here) or for the selected layer.
Anyway, it creates a layergroup with the freqency layers in it just above the selected layer.

The script is somewhat sophisticated

If the separation shall be done for the selected layer, the layer is also moved in the layergroup.
The mode for that layer changes to normal
The opacity for that layer changes to 100%
The mode and opacity is restored for the created layergroup

The separation is done for the whole visible, when
a) "from visible" is selected
b) the selected layer is a layer group

So the separation can be done everywhere in the layerstack.

Hatti

Frequency and/or Color Separation script does the same plus separates color & luminosity and has the same menu path Filters>Generic>Split>.....
Is this the same author?

No, it's not the same author. Sorry, but feel free to change the menu entry.
And it does not the same. The script you mentioned alway makes frequency layers
from the whole visible, not from the selected layer and it uses the gaussian blur.