The Komplete Kontrol S61 is Native Instruments' 61-key MIDI controller keyboard, part of their Komplete Kontrol line aimed at deep integration with NI's software instruments (and other plugins via NKS).

Key features:

• Fatar semi-weighted keybed with aftertouch — a step up in feel from the entry-level A-series
• Light Guide — an LED strip above the keys that shows scales, chords, and instrument mappings in real time
• NKS integration — browse, load, and control parameters of Komplete instruments (and NKS-compatible third-party plugins) directly from the hardware, with a small screen per channel showing plugin/parameter info
• 8 touch-sensitive knobs, transport controls, pitch/mod wheels, and smart plugin/DAW control (Mackie Control-style integration with major DAWs)
• Comes bundled with Komplete Kontrol software plus a selection of instruments from Native Instruments' library

It sits in the middle of the S-series lineup (S49/S61/S88), with the S88 adding a fully weighted hammer-action keybed for piano-style playing. It's generally positioned as a production/studio controller rather than a stage performance keyboard, though it works fine live too.