The only existent method that Unity API is offering is this:

"EditorUtility.ExtractOggFile
static function ExtractOggFile (obj : Object, path : string) : bool

Description

Saves an AudioClip or MovieTexture to a file.

Will save an Ogg Vorbis or Ogg Theora file at the specified path. "

I never used it though, and I never seen it being used before. I hope it helps you. If you want to capture all the sound that you can hear at a specific time in Unity (e.g. multiple sounds playing at the same time) to a single audio file, I don't think there's any method of doing that.

if the unity file is running inside a browser, the audio is not recorded no matter what software you try to use!!!

for mac i can advise you Macvide ScreenCap (macvide.com/Macvide_screencap/), very easy and helpful progfor grabbing screen...

The fraps tool set captures audio and video from any running application, including a Unity game. It's very easy to set up and use.

You can use Soundflower (OS X, free) to route audio as you please. It's more complicated that Wiretap, because you need another app for recording, but it's free and has always worked perfectly for me.

I have never used Virtual Audio Cable, but it's apparently the Windows equivalent of Soundflower.

Also, Audacity runs on OS X, too, and would be an appropriate tool to use with either of these utilities, though it's redundant, given "What U Hear". Although I don't like Audacity, the tools I do like do not offer a simple "What U Hear" choice.