"ZAP" is ZAP! Like a Preston Microforce. It disables zoom-speed, allowing you to make crash zoom adjustments (high speed). When you disable, the joystick reverts to the slow zoom (as set by the zoom-speed knob).
"CAL" is a shortcut to Auto Calibrate all motors.
"MOTS" takes you through to the Motor menu.
"DEBG" and "RXRS" are for services techs and engineers: DEBG makes the controller send constant data (hundreds of packets per second, instead of only sending "changes"). RXRS tells the receiver to reboot itself (we use it to force a Receiver into it's USB bootloader, without having to pull it's power cable).
"DISP" cycles OLED display modes allowing the operator to focus on specific information.