The NanoVNA is an open source VNA project by @edy555 and ttrftech that has recently become extremely affordable at less than US$50 for a fully assembled unit thanks to Chinese manufacturing (or a little more if you order it via Amazon).
Ohan Smit had recently been playing with the NanoVNA and came across a software package from Rune B. Broberg (5Q5R) called NanoVNASaver. NanoVNASaver is an open source program that can be used to read and plot data from the NanoVNA. It has some nice features like the ability to display multiple charts, increase the resolution up to 10k points, measure cable length via TDR calculations, save Touchstone files and more.
Over on his blog, Ohan has put up a walkthrough guide about using NanoVNASaver. He shows how to setup the application, calibrate the NanoVNA, and then demonstrates how to use NanoVNASaver to measure the response of some filters.
Later in the same post Ohan also includes an update about his experiments with some new experimental NanoVNA firmware that extends the maximum frequency range from the previous maximum of 900 MHz up to 1500 MHz. Results show that while it can work up to 1500 MHz, accuracy rapidly degrades above 900 MHz.