Audacity is an audio editing software that is free, open-source and runs on Mac OS, Linux & Windows operating systems. It is a great tool for audio enthusiasts, who wish to get into the basics of audio editing and processing, without spending a dime.
It offers Equalization, compression, fades, tempos, and other basic tools to get you started. The GUI looks childish, however its performance is not. Audacity also supports addition plugins and libraries.
I would recommend this to anyone who wishes to record, edit and mix: lessons, meetings, speeches, practice sessions, gigs, announcements and other small audio jobs.
While, this may be too basic to produce your dream project, it is nevertheless like a swiss army knife in your pocket when you are on the road, with your laptop. I use this to create loops, fades and other program material that I receive for playback at sound gigs.
This is also a great tool for kids. Teach them the basics and let them experiment and discover the world of audio.
Download Link: http://audacity.sourceforge.net/download/