There are several ways you can do Home Automation with a Windows PC via software and usually a PC interface of some sort, though more recently with the cloud the internet and Wi-Fi is the common connection.
Windows IOT Core is just a stripped down Windows (barebones PC of sorts)
Some protocols have APIs or SDKs which anyone with some programing knowledge can create A home automation setup.
I've create several X10 home automation programs though not yet interfaced directly with Cortana.