You can connect multiple "players" to one "recorder." For example, mix Spotify and your microphone into a single feed for a Zoom call.
Supports Windows MME, WASAPI, DirectSound, and KS interfaces. Downloads - Virtual Audio Cable Virtual Audio Cable Free Download
Free but supports only one virtual cable with limited sampling rates. You can connect multiple "players" to one "recorder
Fully functional but adds a female voice reminder every 30 minutes. Download VAC Lite/Trial 🛠️ Key Features Virtual Audio Cable Free Download
This is a commercial product with a limited free version.