PortAudio - PortAudio is a cross platform, open-source, audio I/O library.
Wwise - Game audio engine, designed to give artists more control and save programmers' time.
JUCE - JUCE is a wide-ranging C++ class library for building rich cross-platform applications and plugins...
FMOD - FMOD Studio is an audio middleware solution and engine for games.
OpenAL Soft - OpenAL Soft is an LGPL-licensed, cross-platform, software implementation of the OpenAL 3D audio API.
SoLoud - Easy to use, free, portable c/c++ audio engine for games.