Open Sound System (OSS) is a commercial system for audio drivers for Unix, written by 4Front Technologies (www.opensound.com). There is a GPL implementation of the OSS libraries as well as drivers for many sound cards. (This is called OSS/Free and was originally contributed to by 4Front. Their website says "There is no affiliation between OSS/Free and OSS/Linux anymore except that they are both OSS compatible."). These GPL'd drivers are in the Linux kernel (2.0 and later).
ALSA is a newer project (with a larger scope than OSS). It is in the 2.6 and later versions of the Linux kernel, and has OSS compatibility for older applications and libraries. See AlsaNotes.
Someone did searches on google for how to unmute audio from the command line using aumix(1), so I thought I better write some content about it. Muting in aumix appears to be accomplished by setting all of volume sliders to 0. Unmuting is restoring it to it's saved position. To achieve this from the command line you can save the current settings use "-f /.unmutesettings -S" and then set the master volume to 0 using -v 0. To unmute it aumix "-L -f /.unmutesettings". This is untested.
One page links to AudioNotes:
