The hub that controls the outlets is controlled by a Raspberry Pi Zero W, which connects to my Alexa using Wifi. It sends commands to other devices using an IR blaster modulated at 38kHz. The scripts are written in Python.
To control an outlet, an ATtiny85 is used. It's equipped with an IR demodulator, as well as an SPST relay that controls the flow of the AC electricity going in the appliance to be powered. It uses external pin interrupts to interpret signals coming from the Pi's IR blaster, and powers the relay using a transistor. A re-purposed 5V USB AC adapter is used to power the ATtiny from the AC lines.
To control multiple devices at one location, I chose a Pro Mini since it has more outputs to control more SPST relays. I am currently still designing the casing for this to 3D print, so I don't inadverdently electrocute myself or my cat.