This little ESP8266 board is programmable as a Nodemcu v1.0 or with Arduino IDE and the community plugin(to enter in program mode keep pressed RST, press FLASH, release both).
It is currently selling on Aliexpress as “Witty ESP8266”, and price ranges from 2.60€ to 4€, good ones are in the range of 3€.
It has also a RGB led on pins 12,13,15 , a user button on pin4 and a photoresistor on pin ADC0.
The upper micro USB is for power only, the lower port is for programming it and serial debugging.
It has the nice bonus that you can separe the programmer once done with it and plug it on a carrier board.
You can use it as a “internet button”, by let it to do a get or post request when button is pressed.
Or as a “site down” signal. The RGB led will light green when ping is good, ping is slow, red when ping is missed.
Or as a “light on” in the room alarm. Listen to the photoresistor and when light are up it will send you an e-mail or a message.
It can run with current provided by a usb wall power adapter or a usb power bank.