Pete,
An ST19XL is a processor. This emulates that processor on a pc
running dos, windows or linux. The processor is found in a number of
smartcards, any of which can be emulated if you have the eeprom
(st19.cor) and rom (st19.rom) from the smartcard you are trying to
emulate. Smartcards are used for many things these days and this tool
allows you to test programs written for the smartcard. e.g. Smartcards
used to secure your business can act as keys to unlock a door and keep
track of the time, date and employee number each time the smartcard is
used.
I suggest you download the latest version 2.6.09 and then read the
st19xl.txt file for a more detailed description.