http://audacity.sourceforge.net/

Audacity is very good and usable. If you plan on converting to mp3 you may need to add  the LAME MP3 encoder, hosted by Buanzo.

http://lame.buanzo.org  -  be careful not to 'Start download' on something else that's from one of those ads.

Always scan it with updated antivirus before installing. I recommend Malwarebytes for ondemand scanning.