I have a bit of a soft spot for this kind of application, and this one in particular as it combines an oscilloscope, a real time spectrum analyzer and a signal generator, all of which can run simultaneously. That (in my opinion) is really quite cool!
This is what PocketGear says about it:
Virtins Pocket Instument is a powerful pocket PC based virtual instrument. It consists of a real time oscilloscope, a real time spectrum analyzer and a signal generator, which can run simultaneously. It features a specially designed data acquisition approach which is able to monitor the input signal continuously without missing any trigger event before a frame of data is collected. It supports sophisticated triggering method including pre-trigger and post-trigger. It features zooming and scrolling function and allocates most of the screen for data display, all of which are essential for you to explore the fine details of the measurement data. It provides a comprehensive range of functions including wave form addition, wave form subtraction, Lissajous Pattern display, Voltmeter, transient signal recording, RMS amplitude spectrum display, relative amplitude spectrum display, phase spectrum display, auto correlation coefficient display, cross correlation coefficient display, function generation, arbitrary waveform generation, white noise and pink noise generation and sweep signal generation, etc.
It is also available direct from the developer Virtins.