Audacity is a freeware open source audio editor. As an open source program, there are many different versions.
In this case you can find versions for Windows, Linux and Mac. Also there is a portable version for Windows. This program allows you to record audio using microphone or other input devices and editing the sound.
You can make new projects with multiple channels, synchronize them, add effe, Nyquist analysis etc. It also supports input from audio, midi file. You can add white noise, a tune or silence a channel for some seconds.
Today there are installable and portable Audacity versions for Windows. Portable version can be found on sourceforge as an Audacity zip file. The link is above "system requirements".
This program requires :
Windows 98, ME :128 MB / 500 MHz(recommended) or 64 MB / 300 MHz (min)
Windows 2000, XP :512 MB/1 GHz(recommended) or 128 MB/300 MHz (min)
Windows Vista Home Basic :2 GB / 1 GHz(recommended) or 512 MB / 1 GHz (min)
Windows Vista Home Premium/
Business/Ultimate :4 GB / 2 GHz(recommended) or 1 GB / 1 GHz (min)
For windows, a portable version can be found at sourceforge as "Audacity Zip file".
Download, unzip and run.
Have fun.