Virtual - Audio Cable

does the exact same thing, but entirely in software. It creates a set of "virtual wires" inside your computer. When you send audio to the "output" end of a virtual cable, it instantly appears at the "input" end of the same cable.

Virtual Audio Cable is a software program that creates a virtual audio device on your computer, which can be used to connect multiple audio applications, devices, and services. It allows you to redirect audio signals from one application to another, or from one device to another, without the need for physical cables or complex setup. virtual audio cable

Capture the output of a program (like a web browser or music player) directly into recording software like Audacity, even if the program doesn't allow saving audio. Streaming & Content Creation: does the exact same thing, but entirely in software