This volume mixer by Ananords is based on deej, an open source mixer.
KBD.news Published June 21, 2021
deej is an open-source hardware volume mixer for Windows and Linux PCs. It lets you use real-life sliders (like a DJ!) to seamlessly control the volumes of different apps (such as your music player, the game you're playing and your voice chat session) without having to stop what you're doing.