A calculator with software floating point support from the 1990s. It features floating point numbers with 100+ decimal digits, support for complex numbers and simple CAS capabilities. I wrote this back in high school, growing out of an exercise to solve quadratic equations, and won a prize from the national science competition Schweizer Jugend Forscht.
This is very old code from 1999, written in Turbo Pascal/Delphi and running on 80286 hardware. It uses lots of 16-bit x86 assembly and probably won't compile and run on modern systems anymore. It compiled to a Windows application, which was little more than a simple front-end on top of the underlying CAS engine. Although 32-bit was already available at the time, support was not yet as widespread, which is why I had decided to run with 16-bit.
Unfortunately, all the comments are in German, but on the flipside Pascal is such an easy-to-read language that comments are hardly necessary ;-).