MP3Gain - A free automatic mp3 volume normalizer.
FLAC - A free, open source codec for lossless audio compression and decompression
QMP3Gain - Graphical user interface front end supporting MP3Gain engine which analyzes and losslessly adjusts...
Opus Interactive Audio Codec - Opus is a totally open, royalty-free, highly versatile audio codec.
wxMP3gain - Needs to be compiled.
Vorbis - Ogg Vorbis is a fully open, general-purpose compressed audio format for mid to high quality...