My first major project on the Macintosh was to write a BASIC compiler. I managed to get it to work with little more than MS-BASIC and a copy of the original "phone book" Inside Macintosh documentation.
MockBasic source code
When I was in college, I took a compiler writing class. The main assignment was to write a Pascal compiler. So I wrote it on the Mac using the compiler I had at the time, TML Pascal 2.0. I found a lot of bugs in their compiler while I was writing my own!
Pascal compiler source code
In the early 90's, Buick distributed an adware disk with information on its products. It so happened that the company doing this at the time was in San Antonio. I ended up writing the code for the Macintosh versions of the 1990 and 1991 demos using Object Pascal.
I first worked on the '89 version, when they were having problems with their Mac programmer at the time. When I knew the '90 version was going to happen, I spent two weeks of my own time writing a Hypercard-like application framework in Object Pascal. After I was hired, I wrote the rest of the framework: a WYSIWYG editor and a Hypercard-like programming language.
Here are runnable copies of both of them:
(requires binhex decoder and 68K or PPC Macintosh with MacOS 6.x-9.x or OS X Classic)
buick-92.zip - source code (I'm not sure why it got named 92)
One of my computers was a Mac IIci, for which I had gotten a TokaMac 68040 accellerator card. But the software for the card didn't include any code to patch the Memory Manager to work correctly with the 68040. While it was long after the company had made the card was out of business, and I had already gotten a PowerPC Mac, I dissassembled the code from a 68040 Mac and made a patch for the Memory Manager.
TokaMMInit.zip full source code and a MacBinary-encoded INIT file
This is a video subtitling program for the Mac. I actually got it finished and useful, but I had to give up on it because I didn't have good enough video hardware to use with it.
SubApp source code
Here is a 68000 assembly language subroutine that I coverted to PowerPC assembly language.
crypt.c (PPC translation)