audiorouterdev/audio-router

Audio Router is a free Windows desktop application that lets you send the audio output of individual programs to different audio devices on your computer. By default, Windows sends all sound through one output device at a time, so if you want your music player to go through speakers while a game goes through headphones, you normally cannot do that without paid third-party software. Audio Router solves that problem without a purchase. The app shows a list of running programs that are producing audio, and you can pick each one and choose which device it should route its sound to. You can also duplicate an audio stream so that it plays through multiple devices at the same time, which is useful if you want the same audio heard on two different outputs simultaneously. Starting with version 0.10, Audio Router can save your routing choices for a given application. When that program launches again with Audio Router already running, it will be automatically routed to the correct device without you needing to set it up again each time. The README notes that this does not work for applications that need administrator rights. The application runs on Windows 7 and later, and requires administrator rights to start. Both 32-bit and 64-bit versions are available as direct downloads from the GitHub releases page. The source code is also publicly available. The README lists a few known interface bugs, such as scroll bars slightly overlapping other elements and some unused audio sessions remaining in the Windows volume mixer after routing. The project is maintained by an independent developer who accepts feedback and bug reports.