This is free software that is readily available on the internet. It is supposedly easy to use. Many of the ghost websites I have visited recommend using this software to take EVPs off your tape or digital voice recorder and use to review and enhance in order to pull out the EVPs. I've not used it at all for EVPs but have experimented a bit with just recording audio.
This link has some great info on using Audacity.
http://audacitybook.org/html/This is the link where you can download it if you like:
http://audacity.sourceforge.net/Does anyone have any experience using Audacity to enhance and listen to EVPs?
Jim