Rudolph thought it would be nice to have one radio transmitter that could talk to all of his creations, so he created rudRemote.
rudRemote uses a NRF24L01+ radio module and a Teensy 3.2 to interface the controls. Almost any type of housing can be used. In this case Rudolph used a 40-year-old transmitter that he found and added an OLED display. The controller uses CRTP (Crazy RealTime Protocol) so he could use it to fly his CrazyFile quadcopter.
This HackADay article also talks about the project.
Code for the project can be found on GitHub.