Topic: LineIn for OS X enables the soft playthru of audio from input devices.

[Software Santa]

LineIn is a simple application for OS X to enable the soft playthru of audio from input devices. 

LineIn:

LineIn is a simple application for OS X to enable the soft playthru of audio from input devices. In simpler terms, you can use LineIn to play sound coming in through a microphone or any other device plugged in to your Sound In port, just as was once available with OS 9's "Play input through output device" option.

Version: 2.0.3 (October 19th, 2007)
Operating Systems: OS X 10.4.0 - 10.5.2
Architecture: PowerPC, Intel

http://rogueamoeba.com/freebies/