Audacity

Audacity® is free, open source software for recording and editing sounds. It works on Windows, Mac OS X, GNU/Linux, and other operating systems. Learn more about Audacity at http://audacityteam.org. Audacity can record live audio through a microphone or mixer, or digitize recordings from other media. Import, edit, and combine sound files. Export your recordings in many different file formats, including multiple files at once. Supports 16-bit, 24-bit and 32-bit. Sample rates and formats are converted using high-quality resampling and dithering.

Easy editing with Cut, Copy, Paste and Delete. Also unlimited sequential Undo (and Redo) in the session to go back any number of step and more.