An ESP8266 is a wifi capable microcontroller. The ESP-01S is a minimal version of that controller which can be cheaply integrated into internet of things projects. This relay module is designed for and is sold with the ESP-01S module. The relay can turn a circuit on or off and is capable of controlling an AC load.
A program can be created which will allow this module to connect to the internet or LAN and be controlled by any other device on that network. It could be a server controlling thousands of devices, a smartphone app, or a physical device on the local network.
The most apparent solution is to use this module to turn a light on or off in a smart home. The relay module could be used in other ways such as collecting data from a garden using other sensors and then turning on a pump when needed to water plants. Since this is wifi connected a central server could be used taking into account other variables like upcoming weather and then making an intelligent decision on whether the pump should be turned on or not.
2 x ESP-01S Compatible Relay Module
2 x ESP-01S