Did you even look at those .abr brushes ?
Everything might have been Gimp scripts 10 years ago with Gimp 2.8 - neon text or alpha neon - but those are long gone.
Using additions to basic Gimp. If you want a plugin for neon there is the gimp_gmic_qt plugin, http://www.gmic.eu
For smoke painting in an overlay layer with layer mode luma lighten
Everything might have been Gimp scripts 10 years ago with Gimp 2.8 - neon text or alpha neon - but those are long gone.
Using additions to basic Gimp. If you want a plugin for neon there is the gimp_gmic_qt plugin, http://www.gmic.eu
For smoke painting in an overlay layer with layer mode luma lighten