See my early work: X-Debug from 1992
I recently discovered a floppy containing the source to a program I wrote in 1992: X-Debug, a debugger for the Atari ST. Coincidentally I also received an email via this blog from someone asking if I had the source and rights to the Atari version of HiSoft Devpac, which I wrote in the late-80s. I couldn't help with Devpac, but I have posted the full source to X-Debug on my personal site.
Its interesting to look at my code from way back then: it was mostly in C, which a bit of assembler for the low-level stuff (screen access, MMU hackery, debugger hooks). Apart from the formatting, and the fact it is C and not C++, it's not too bad, though I say so myself.
Somewhere I have a 10M (yes thats megabyte) SCSI hard-drive that contains everything I did for the Atari. If I could find it, and if it still works, I could dig up some more old stuff from this period of my life, as it is FAT-formatted so a PC should read it. I even have an Atari ST emulator somewhere so I guess I could even run the stuff on my PC too.