TL;DR - Visual Analyzer, PC Sound Card Oscilloscope software. Nice spectrum analyzer. Worth checking out. http://www.sillanumsoft.org/prod01.htm
Through a really good YouTube Post on using an SDR for Frequency Deviation Measurement on FM transmitters I learned about Visual Analyzer. I should probably do a separate post just on this.
Previously I used Xoscope on Linux and Zeitnitz Soundcard Oscilloscope (http://www.zeitnitz.eu/scope_en).
I had also found, but not used Zelscope, Soundcard Oscilloscope and Spectrum Analyzer.
I originally got some pointers on sound card osclloscopes, from Virginia Tech's Introductory Electronics courses that were based on their Lab in a Box, so that students would have all of their own materials for doing the electronics work without having to be in a physical lab. See:
Virginia Tech, Experiment 12, Calibrating a Sound Card Oscilloscope
I only went so far with sound card oscilloscopes, because shortly after I started experimenting, the Rigol DS-1052E oscilloscope became available within my budget. I bought it for $400 direct from China. The Rigol caused a little bit of a revolution in terms of oscilloscope availability and pricing.
That was all back in 2009 and 2010 when I started reading a lot more about electronics. In December, 2009, I finally took the exams from my amateur radio license. I passed both Technician and General with 100% and went back for the Extra Class at the next exam session. I got one wrong on my Extra.
Of course, the interesting bit that got me here writing this today is that the RTL-SDR stick can be used as the analog (ok radio frequency) front end for a software oscilloscope, spectrum analyzer, deviation meter, etc. Especially for those of us without much in test equipment.