RtAudio!

JUCE has hundreds of classes covering a vast range of tasks from high-level user-interface handling right down to low-level collections, networking, strings, etc. Supported platforms are OSX, Windows, Linux, iOS and Android, and the Introjucer project management tool makes it a breeze to create and maintain cross-platform projects.

"Wwise® is the most advanced, feature-rich interactive sound engine for games, bar none. Whether you're an indie or a multi-million dollar production, Wwise will work for you." - Audiokinetic.com

PortAudio is a cross platform, open-source, audio I/O library. It provides a very simple API for recording and/or playing sound using a simple callback function.

FMOD is a proprietary audio library that plays music files of diverse formats on many different operating system platforms, used in games and software applications to provide audio functionality.

OpenAL Soft is an LGPL-licensed, cross-platform, software implementation of the OpenAL 3D audio API. It's forked from the open-sourced Windows version available originally from the SVN repository at openal.org.OpenAL provides capabilities for playing audio in a virtual 3D environment. Distance attenuation, doppler shift, and directional sound emitters are among the features handled by the API. More advanced effects, including air absorption, occlusion, and environmental reverb, are available through the EFX extension. It also facilitates streaming audio, multi-channel buffers, and audio capture. »