Arduino Uno or Nano generates 244-8,000,000 Hz by dividing the 16 MHz crystal oscillator. The pushbuttons set the division from 0 to 255 holding the button advance the frequency every second.. The high frequency output at pin 6 is 8000000 / (division + 1) , the low frequency output at pin 11 is 62500 / (division + 1). Division is by integer so not any frequencies can be set, for example the High Frequency output can be 8, 4, 2.666, 2, 1.6, 1.333 MHz etc. The LCD of 16x2 display the High and Low Frequencies. The LCD module has to be HD44780 compatible.
The software is for Arduino with ATMEGA328. The outputs are generated by using Timer2 and Timer0 in CTC mode.