The first sketch used to test an Arduino compatible board is Blink.
After run Blink in my new NodeMCU Development Kit,
Started experiments with the WiFi connection:
-Mini servers to control leds, servos, etc..
-Send light intensity and temperature to ThingSpeak, Xively, Plotly etc..
-Serial data bridges

The blue led in the board was used to signal the execution of a particular procedure.
Because the GPIO16 (DO) limitation to use the analogWrite() and looking to see my LED doing something else…

Inspired by the Apple’s “breathing” pattern used for the sleep indicator.
Here is the code to generate a “breathing LED”.

The Arduino code runs inside a multitasking application, the ESP8266 is running at the same time TCP and WiFi stacks.
The sketch can breake the multitasking execution if your code runs in a blocking section.
The delayMicroseconds() is one of those blocking functions, delay(0)  was used to prevent watchdog reset inside the PWM loops.

/*LED_Breathing.ino  20 AUG 2015
Using NodeMCU Development Kit V1.0
Going beyond Blink sketch to see the blue LED breathing.
A PWM modulation is made in software because GPIO16 can't
be used with analogWrite().

#define LED     D0        // Led in NodeMCU at pin GPIO16 (D0).
#define BRIGHT    350     //max led intensity (1-500)
#define INHALE    1250    //Inhalation time in milliseconds.
#define PULSE     INHALE*1000/BRIGHT
#define REST      1000    //Rest Between Inhalations.

//----- Setup function. ------------------------
void setup() {                
  pinMode(LED, OUTPUT);   // LED pin as output.    

//----- Loop routine. --------------------------
void loop() {
  //ramp increasing intensity, Inhalation: 
  for (int i=1;i<BRIGHT;i++){
    digitalWrite(LED, LOW);          // turn the LED on.
    delayMicroseconds(i*10);         // wait
    digitalWrite(LED, HIGH);         // turn the LED off.
    delayMicroseconds(PULSE-i*10);   // wait
    delay(0);                        //to prevent watchdog firing.
  //ramp decreasing intensity, Exhalation (half time):
  for (int i=BRIGHT-1;i>0;i--){
    digitalWrite(LED, LOW);          // turn the LED on.
    delayMicroseconds(i*10);          // wait
    digitalWrite(LED, HIGH);         // turn the LED off.
    delayMicroseconds(PULSE-i*10);  // wait
    delay(0);                        //to prevent watchdog firing.
  delay(REST);                       //take a rest...