Sound Recording Application that Starts/Stops Automatically

I'm looking for a sound/voice recording application that I would just let run on my PC all the time. It would either start/stop based on whether there is "anything worth recording" or maybe just record constantly but discard silent segments.

EDIT

If you have OS specific suggestions, Windows would need to be supported. Of course, if your solution only works on other OSes I'd like to hear about them anyway.

Solution 1:

GoldWave will do level-activated recording. It's not free, but I tried dozens of audio editing apps before settling on it, have used it for years, and have found it to be excellent value for money.