Audacity Portable is the popular Audacity audio editor packaged as a portable app, so you can take your audio files along with everything you need to edit and record on the go. It is a free and open source audio editing application that's portable and user friendly.
Here are some screenshots to illustrate the features and user interface of this application:
Wavepad Audio Editor
Wavepad Free
REAPER
n-Track Studio
Audacity