Buchla Thunder is one of many in the family of MIDI controllers consisting of tactile control surfaces, which are manipulated by hand.
The Thunder features a touch-plate array of fifty separate regions, or keys. Keys are sensitive to the contact, pressure, and location of a player's fingers. The player can assign parameters to produce a desired output. Thunder is a pure MIDI controller, with no internal sound generator of its own.
References
Buchla Thunder Wikipedia(Text) CC BY-SA