This is a custom-built keyboard. It features a trackball, eliminating the need to move your hand to operate a mouse, which helps prevent tenosynovitis and improves work efficiency. I'm selling it because I couldn't get used to it. Condition: Tested and working. It's in excellent condition, almost new, with only a few test uses after assembly. It allows for a natural typing posture that reduces strain on the shoulders and arms. Trackball: Equipped with a high-precision trackball on the right side, enabling mouse operation in a space-saving manner. [Included Items] Keyboard body (left and right units) TRRS cable (for connecting left and right units) USB Type-C cable (for connecting to PC) Trackball [Other] The keyboard was assembled carefully, but it is a custom-built item, so please purchase only if you understand this. I made it with the help of a friend, so I don't know the specifics, but I believe it's a Keyball39. Immediate purchase is welcome, and price negotiations are also negotiable.