This is my 3D printed WASD Keyboard. 

Parts needed:

• Arduino pro micro (only works with Arduino pro micro oder leonardo)
• 4 Keyboard switches
• some wire
• 4 Keycaps (mine are from @misterryan)

Wirering:

[Switch W] ───── Pin 2
      └──────── GND

[Switch A] ───── Pin 3
      └──────── GND

[Switch S] ───── Pin 4
      └──────── GND

[Switch D] ───── Pin 5
      └──────── GND

Code: 

#include <Keyboard.h>

const int wPin = 2;
const int aPin = 3;
const int sPin = 4;
const int dPin = 5;

void setup() {
 pinMode(wPin, INPUT_PULLUP);
 pinMode(aPin, INPUT_PULLUP);
 pinMode(sPin, INPUT_PULLUP);
 pinMode(dPin, INPUT_PULLUP);

 Keyboard.begin();
}

void loop() {

 // W
 if (!digitalRead(wPin))
   Keyboard.press('w');
 else
   Keyboard.release('w');

 // A
 if (!digitalRead(aPin))
   Keyboard.press('a');
 else
   Keyboard.release('a');

 // S
 if (!digitalRead(sPin))
   Keyboard.press('s');
 else
   Keyboard.release('s');

 // D
 if (!digitalRead(dPin))
   Keyboard.press('d');
 else
   Keyboard.release('d');

}