Emu48 for the mac is a saturn based HP calculator emulator.
This port is based on emu48 SP25 ( running on win32 plateform)
which can be found on Christoph Giesselink 's home page
The MacOSX Version is now maintained by Da Woon Jung on emu48mac.sourceforge.net
To run this emulator you will need 2 archives:
The emulator itself
And some calculator specific files.
Emu48 is gpl'd
you can find the sources here
Related links:Home page of the original version of emu48
you will find there many emu48 related information such as a faq
hp48 software archive