“I have a drawer of random electronics parts and failed dreams. Amongst this pile is a handful ESP8266 chips. These devices are intended to be used as low-cost WiFi modules which are operated by other microprocessors, and by default you can communicate with them over UART with a variety of commands (join a network, send a packet, etc). The idea is that you solder one of these onto your project and voila! you now have connectivity in your project. On their own, they are pretty neat. They are super cheap (~$2 on Aliexpress) and super simple to use (UART). But the real key is that you can re-flash these devices to run your own code. So instead of a “dumb” WiFi module that’s controlled by another microcontroller, you get a microcontroller that has WiFi built in, with access to all the GPIOs, I2C, SPI and ADC.”