Applescript gadget that politely saves volume/mute settings, unmutes, sets volume very low, whispers some text provided on the commandline (the first CLI argument only) then politely restores the volume/mute settings. Polite!
Don't install this to unattended MacBooks. Definitely don't make it run as a cron job...
chmod +x whisperer.osascript
./whisperer.osascript 'please be quiet! this is a library'