when you use google then you will see that there are 5 free ones
for dowload and use.
JackAudio
Take the audio output of one piece of software and send it to another.
JackAudio is a virtual audio software cable that run on Windows Linux and MacOS and if Free to download and to use.
Virtual Audio Capture Device
This software is a free windows audio capture driver that allow you to capture all the wave-out-sound that is playing on your speakers,
and will record what you hear.
Runs on XP, Windows 7 and Vista.
VB Cable
VB-Audio CABLE is a Windows Audio Driver working as Virtual Audio Cable.
Will allow you to connect Audio Software together with Virtual Audio Device, to record input of streaming software.
Vsound
Vsound is a Linux software which allows you to digitally record the output of another program.
The recorded output can be saved to a WAV file or can be transferred into another software.
It's basically an audio transfer cable software.
You must be registered for see links
SoundFlower
Soundflower is a Mac OS X (10.2 and later) system extension that allows applications to pass audio to other applications.
Soundflower is easy to use, it simply presents itself as an audio device,
allowing any audio application to send and receive audio with no other support needed. Soundflower is free.
