Transmit / receive uncompressed stereo audio over a local network. Turn two Macs into a really expensive XLR cable… for free!

DGuitar is a Guitar Pro (*.GP4,*.GP3,GTP) viewer and player that works under Linux, MacOs, Solaris, BSD or Windows or any other Operational System that has Java Runtime Environment 1.4 or later installed.
The Twonker is a free VST MIDI Plugin that allows a digital piano (or any MIDI instrument) to play tones from the Overtone Series. It is designed to run within most Digital Audio Workstations as a Synth Plugin on MacOS, Windows, and Linux.
The Twonker allows a musician to play overtones in a predictable and flexible manner, using a regular MIDI-based keyboard. In essence, it behaves like twelve different pianos tuned to twelve different “Overtone Scales”.

AUDio MEasurement System – multi-platfrom system for audio measurement through a PC sound card. Incorporates generator, oscilloscope, audio spectrum analyzer (FFT) and frequency sweep characteristic. Can be compiled and works under Linux, Windows and MacOS.

sourceforge.net/projects/audmes
en.wikipedia.org/wiki/Spectrum_analyzer
en.wikipedia.org/wiki/Oscilloscope
Athletes’ companion: adds synthesized voice overlay with various info and on-going timer to your audio files.
Features:
github.com/MarcinOrlowski/Mp3VoiceStamp
A cross-platform, multi-format audio conversion and tagging suite for .NET and PowerShell. Formats currently supported are MP3, MP4 AAC, FLAC, Apple Lossless (ALAC), Opus, Ogg Vorbis and Wave.
This project supplants PowerShell Audio by targeting both Windows PowerShell and PowerShell Core (Windows, Linux and MacOS).
Soundsync is a web and desktop app to manage every audio source and every audio output in your home from a single interface. Link any audio source to multiple speakers connected to any devices on your home network. Soundsync will keep the music synchronized between all of them.
Features:
- 🆓 Free to use
- 🕸️ Work with any number of connected devices, audio sources, audio outputs and every link of your choosing
- 🎶 Compatible with a lot of different audio sources (Spotify Connect with a premium account, Airplay, Hardware Audio input (line in / microphone), Linux system audio ; coming soon: Windows system audio, UPnP and more)
- 🔊 Broadcast sound to any speaker connected to a computer (Windows, MacOS, Linux, RapsberryPi), a web browser (Chrome, Firefox) or a Chromecast and soon more
- 🔗 Group speakers together to synchronize them to the same audio source
- 🎛️ Control everything from a web browser
- 🔓 Not linked to any external service, works offline, no account creation
Shairport Sync is an AirPlay audio player – it plays audio streamed from iTunes, iOS, Apple TV and macOS devices and AirPlay sources such as Quicktime Player and ForkedDaapd, among others.
Audio played by a Shairport Sync-powered device stays synchronised with the source and hence with similar devices playing the same source. In this way, synchronised multi-room audio is possible for players that support it, such as iTunes and the macOS Music app.
Shairport Sync runs on Linux, FreeBSD and OpenBSD. It does not support AirPlay video or photo streaming.
github.com/mikebrady/shairport-sync
github.com/mikebrady/shairport-sync/wiki
Andes is a standalone software synthesiser, or plugin, in early stages of development. The core of Andes is an original oscillator which uses a pseudo-3D version of Perlin Noise to produce distinctively digital sound.

BlackHole is a modern macOS virtual audio driver that allows applications to pass audio to other applications with zero additional latency.

existential.audio/blackhole
github.com/ExistentialAudio/BlackHole
- Automatically pauses your music player when other audio starts playing and unpauses it afterwards
- Per-application volume, boost quiet apps
- Record system audio
github.com/kyleneideck/BackgroundMusic
awesomeopensource.com/project/kyleneideck/BackgroundMusic