Field Link Portable Programmer from Castle Creations - 010-0063-01
Field Link Portable Programmer allows you to modify the most commonly used settings in your Castle controller at the touch of a single button.
Field Link for Flying settings:

Cutoff voltage
Auto LiPo volts per cell (3.0, 3.1, 3.2, 3.3, 3.4, 3.5)
Low voltage cutoff type
BEC voltage setting*
Motor timing*
Motor direction
Throttle type*
Brake
Governor gain*

*If applicable to your ESC.
Specifications: