Linux software: EarCandy
EarCandy – the PulseAudio sound manager is a small tool that is located in tray bar, watch all open applications, and instead of you manage with sound. Here are a few examples of how the program works: suppose you listen a music in Amarok, but at the same time rings Skype – this tool will (gradually, and depending on settings) reduce the tone of Amarok sound and give priority to bell from a Skype call, which was only “playing” in the moment. Or, while you listen a music and surfing during the encounter interesting YouTube videos – no problem, EarCandy reduce the tone of music player until YouTube video finishes. These are just some examples, the thing works with other programs like video players or other programs that you can arbitrarily add.
EarCandy have very practical interface GUI, while the program is performing excellent work for which it is intended. You can download it on the official web site.
In order to get the best insight to the whole thing works, maybe it is best to see this video.