When Gustavo González and I started writing QAntenna, one of the ideas we had is to write a Smith chart in order to be able to plot the frequency sweep of the antennas. We looked for similar libre software programs and we found linsmith (wich happened to be maintained for Debian by Margarita Manterola). The program is excellent, but it had some drawbacks: the chart is not resizable (it's an image) and it's very pixelled. So I decided to write a Smitch chart class with Qt.
Of course, I havent give it enough time as it deserves, but it's slowly improving:
It turned out to be useful as a separate program, specially for students learning how to use the chart, so I created QZPlot. It is more than alpha, but I hope to find the time to get it to 1.0 :-)