Front and rear derailleurs are servo controlled. These connect to a central unit that also has the shifters connected to it. This central unit can communicate with a bike computer (via ant+) to show gearing.
In addition, you can set it up so that when you shift the front derailleur, it automatically moves the rear derailler. You might want to do this in order to keep roughly the same gear ratio when changing chainrings. Or, there is a mode where you just shift up and down, and the system manages the shift for you, shifting either (or both) derailleurs, simulating a 1x drivetrain.
All of the popular group sets have a version of this: shimano, sram, and campagnolo.