Recently I wanted to remotely turn on/off a device which is connected to a wall outlet. Building an RF transmitter and a receiver was an option, but why build two separate RF units when we already have WiFi all around us.
So, instead of trying to integrate WiFi capabilities into the device, I've decided that it is more useful to build a wall outlet adapter which can be controlled over WiFi.
Since I had several of these universal travel adapters lying around, I used them as reference for my designs.
Diagram: