ALSA (Advanced Linux Sound Architecture)
An audio library (and kernel level API) for Linux.
BruteFIR
A software for applying long FIR filters to multi-channel digital audio, either offline or in realtime.
Digital Room Correction
DRC generates digital room correction FIR filters to be used within HiFi systems in conjunction with real time convolution engines like BruteFIR. [Aladdin Free Public License (AFPL)]
DMM_Volume_DLL
The control of volume is realized by the u32 library. The library can work in all the MS Windows versions (95, 98, ME, NT, 2000 and XP). [Commercial]
DUMB - Dedicated Universal Music Bastardisation
A high-quality IT/XM/S3M player library. Versions 0.9+ will have MOD support. An add-on is available for playing OGG files. [Freeware]
Ethan Brodsky's Sound Programming Libraries
Sound libraries for the PC-DOS platform.
GSI (General Sound Interface)
An audio system with network support and provides the ability to use stereo, 3D audio, doppler effects, music playing (MIDI, HMP, MUS), and cd playing and ejecting/changing. [Open source, BSD License]
Imtelephone.com
Provide the audio/video codec Win32 static linked library with source code implement ITU G.722, G.723.1, G.729a, G,728 which support multi-channel concurrent. Also provide the audio arithmetic such as AEC, VAD, AGC, VoiceXML. [Commercial]
OpenAL
A free (LGPL-ed) and open source, cross platform audio library used for 3D and 2D sound.
Spark
A sound engine for Windows. It provides powerful sample, streaming, and module playback functions and can be used with and without DirectSound. It distributed in two forms: static (.lib) or dynamic (.dll) libraries.
Virtual Sampler SDK
Provides applications running on Pentium-class PCs under MS Windows 9x/NT/2000 with a MIDI-controlled, low-latency, fully programmable wavetable module implemented entirely in software. [Commercial]