AudioBus!

Soundflower is a Mac OS X system extension that allows applications to pass audio to other applications. Soundflower is easy to use, it simply presents itself as an audio device, allowing any audio application to send and receive audio with no other support needed. Soundflower is free, open-source, and runs on Mac Intel and PPC computers.

JACK is a professional sound server daemon that provides real-time, low latency connections for both audio and MIDI data between applications that implement its API.

Ever wanted to record your speaker output? (loopback) This is for you. It makes tinkering with the audio of each individual application much easier. As well as being able to loop-back.

VB-Audio CABLE is a Windows Audio Driver working as a Virtual Audio Cable. After installing the VB-CABLE driver, a new playback device appears in the audio device list and can be set as default device. VB-CABLE can be set as the default device, just like any regular audio device. The Configure and Properties buttons allow to setup multi-channel features and device sound quality. All signal coming in the CABLE input is going to the CABLE output. This makes it simple to record the audio stream using some other application. »

PulseAudio is a sound system for POSIX OSes, meaning that it is a proxy for your sound applications. It allows you to do advanced operations on your sound data as it passes between your application and your hardware. Things like transferring the audio to a different machine, changing the sample format or channel count and mixing several sounds into one are easily achieved using a sound server.

Suddenly, it's easy to pass audio between applications on your Mac. Create virtual audio devices to take the sound from applications and audio input devices, then send it to audio processing applications. Loopback gives you the power of a high-end studio mixing board, right inside your computer!

Voicemeeter Banana can mix audio from audio devices as well as from audio applications, in the form of a virtual soundcard. It is an enhanced version of Voicemeeter. Voicemeeter Banana can also route audio over the network using VBAN. A netwroked audio protocol used in VB-Audio software.

Carla is an audio plugin host, with support for many audio drivers and plugin formats. It has some nice features like automation of parameters via MIDI CC (and send output back as MIDI too) and full OSC control.

Advanced Linux Sound Architecture (known by the acronym ALSA) is a free and open source software framework that provides an API for device drivers for sound cards. Some of the goals of the ALSA project at its inception were automatic configuration of sound-card hardware, and graceful handling of multiple sound devices in a system, goals which it has largely met. A couple of different frameworks, such as JACK, use ALSA to allow performing low-latency professional-grade audio editing and mixing.

virtual-audio-capture-grabber-device is an audio capture device allowing you to capture all the "wave out sound" that is playing on your speakers (i.e. record what you hear) for Windows 7/Vista.

Vsound a virtual audio loopback cable - Vsound is an application which allows you to digitally record the output of another program such as RealPlayer. The recorded output can be saved to a WAV file or can be piped into another program such as an MP3 encoder.

Dante Via can intercept the audio from your professional audio applications and makes those application's inputs and outputs available to the Dante network. You can use two copies of Dante Via to interconnect two ordinary PCs or Macs and share audio between them. Or you can interface your audio apps with professional Dante audio gear, over the network. Dante via can also expose your computers audio inputs and outputs to the Dante network.

Dante Virtual Soundcard turns your computer into a Dante-powered workstation, seamlessly integrating your PC or Mac with Dante audio devices on your network. Since Dante doesn't require any special network hardware, all you need is a common ethernet interface.Dante Virtual Soundcard creates virtual (ASIO and MME on Windows, CoreAudio on Mac) soundcards on your system, that can be routed in your Dante network. If there is no dante hardware or Dante VIA in your network, DVS can't be used between 2 computers, this is because DVS can't be the clock master of a Dante network. »

Synchronous Audio Router is a software-based audio routing driver for Windows. You can create any number of Windows audio endpoints, either playback or recording, and route them using any digital audio workstation software which supports ASIO, all with low latency. Even applications with no ability to select audio devices are supported using per-application default device overrides.