Another interesting commercial package is the one available from Zelscope, and a 14-day trial version can be downloaded from their website at http://www.zelscope.com/.
This is a commercial package but it has some very useful features. The main window looks very much like (and has many of the same features as) an actual oscilloscope.
The Zelscope oscilloscope window
The software has a number of useful modes including an audio spectrum analyzer. The following screenshot shows the same 1 KHz sine wave shown in the preceding screenshot in the spectrum window:
The Zelscope spectrum window
