Audacity Audio Editor and Recorder

Audacity is a free downloadable audio editor and recorder, compatible with for Windows, Mac OS X, GNU/Linux and other operating systems. Use it to record live audio, podcasts, convert tapes and records into digital recordings or CDs, and edit Ogg Vorbis, MP3, WAV or AIFF sound files. You can cut, copy, splice or mix sounds together, or change the speed or pitch of a recording.

This support community for this software is extensive, and the site has detailed documentation and tutorials, with many more on Youtube and Vimeo.