You can modify the properties of an audio file such as the sampling rate or sample size, adjust the speed, link one file with another or mix two files into one. These are just some of the operations that can be performed with the program.
The list of formats that SoX Sound eXchange can handle is very extensive. It includes, among others: MP3, MP4, OGG Vorbis, FLAC, Amiga, WavPack, WAV, VOX, VOC, Yamaha, Apple, etc. It offers the following effects: Chorus, Delay, Echo, Flanger, Phaser, repeat, reverb, reverse, fade, gain, silence, trim, bend, pitch, stretch, dither and many more. See the full list at here.
It comes with a PDF manual that explains how to run this tool from the command line.