Big support for f.lux, when you bypass it at night you see the difference
A very cool piece of software i'm using all the time on osx is audiofinder, altough not freeware it allows you to see the waveform in realtime, reads .flac and other lossless formats
and has other nice features such as bulk renaming for extensive audiofiles lybraries
http://www.icedaudio.com/site/