Processing

// Example by Tom Igoe

import processing.serial.*;

Serial myPort;  // The serial port:

void setup() {
  // List all the available serial ports:
  printArray(Serial.list());
  // Open the port you are using at the rate you want:
  myPort = new Serial(this, Serial.list()[0], 9600);
  myPort.write(45);
}

void draw() {
  while (myPort.available() > 0) {
    char lastIn = myPort.lastChar();
    println(lastIn);
  }
}