This instrument works similar to RADAR for high-speed signal paths: It performs time domain reflectometry (TDR), i.e. it sends a step into the path (cable, printed circuit board trace or other) and measures the reflection signal over time. From that one can deduce faults, imperfections, discontinuities and other features of the signal path.
The Picaxe 28X controls the signal generation and the sample circuitry, digitizes the analog measurements, and transmits the data to a PC running the acquisition software. The time scale is measured in picoseconds, and the effective signal bandwidth is over 2 GHz!
I use this as a demonstration tool for my seminars, and it is also sold commercially.