"PulseAudio's impressive set of features include
per-application volume controls, a modular architecture, support
for multiple audio sources and sinks, the ability to discover other
computers using PulseAudio on the local network and play sound, as
well as change which output device an application plays sound
through -- while the application is playing sound.
"Thanks to PulseAudio, the Linux audio experience will become
more context-aware. For example, if a video is running in one
application the system should automatically reduce the volume of
everything else and increase it when the video is finished."