Download of wxmp3gain-v3.1-win32-setup.exe (wxmp3gain-v3.1-win32-setup.exe ( external link: SF.net): 4,210,614 bytes) will begin shortly. If not so, click link on the left.
wxMP3gain is a free front-end for the MP3gain.
For ubuntu users:
sudo add-apt-repository -y ppa:cfgnunes/ppa
sudo apt-get update
sudo apt-get -y install wxmp3gain