I was always curious about the Apple II. When I went back for grad school,
I found the Apple //e Technical Reference Manual in the bookstore, so I
wrote an emulator for it which ran under Unix. There were ROM listings
in the back of the manual, so I typed them in and wrote an assembler so
I would have a ROM for the emulator (no BASIC, though). It worked--I could
run diagnostics and enter the mini-assembler.
Shortly afterwords, I bought a Laser 128/EX. I was able to capture its
ROM and converted my Apple //e emulator into a Laser 128/EX emulator.