This name appears to be from a – possibly a free Kontakt instrument shared on forums (e.g., PianoWorld, VI-Control) or a preset pack for Kontakt. It may also be part of a collection like "Kollection Keys" by a small developer.
The heart of NK Stage is its 4-layer velocity switching. Most budget libraries use two layers (soft/hard), leading to mechanical transitions. NK Stage interpolates between Soft , Medium , Hard , and Fortissimo strikes. The result is a dynamic range that responds to your playing fingers—not just MIDI velocity numbers. kollection keys nk stage full version kontakt work