Noob: Control stuff from PC

Hi everyone. Total noob question.

If I want to use a SFF PC centrally to control multiple things (instead of having e.g. RspbPI at each location), how do I do that?

Let's say the PC is patch cabled onto wifi router - is there some sort of a wifi-to-I/O thing that I can install at end point that can be commanded by like a py script? For example I have two greenhouses with various compinents such as temp guage in, solenoid valve out.

Thanks