Audacity

Audacity is a free, open-source audio file editor. Make your own music mixes or sound edits with this handy program. I don't use this program very often, mainly because I don't have a need for it, but I do recognize it's power.

Audacity can be used to record audio, convert tapes and records into digital recordings or CDs, or edit Ogg Vorbis, MP3, or WAV files. You can also cut, copy, splice and mix sounds together, change the speed or pitch of a record. And that is just for starters.

Audacity runs on Windows, Linux and Mac OSX.

Check out the Audacity website