I have been writing test/diagnostic/bench tools from very early on in my career. Many of these tools have been and are still being sold through my mail order company "Dunfield Development Services".
These are described on my Network and Communication page:
I've done a number of simulator as test tools, some of these are described on my Simulators and Emulators page:
PCLA is a PC based logic analyzer using the parallel port as the input device. It can capture 13 channels with a 500khz sample rate. It includes trigger match (0/1/don't care) for all channels, a 256 entry pre-trigger display and can store and review up to 65536 samples following the trigger event.
LineScope is a PC/sound-card audio frequency digital storate oscilliscope with extra diagnostic features. It can capture, store, display and analyze audio frequency waveforms, as well as create and play custom audio waveforms. It features an echo analysis mode where the created waveform is played, and the echo from the network is immediately captured. It has a wide range of display options, including bounded operations, magnification, absolute or relative scale, off-screen indicators and other features.
I've developed loaders and bootstrap utilities for virtually every embedded system I've worked on (which has been many). In some cases, these work in conjunction with an on-chip bootstrap facility provided by the vendor, in other cases they rely on a small bit of resident bootstrap code developed as part of the loader. These are usually small command line tools which can be automated in testing scripts (versus the vendor supplied "point and click" loaders which require human intervention every time you reload the system... which can happen many times during a development session).