Ever think about your operating system? Sure, there are several layers, like an onion, but the one most users interact with is the Graphical User Interface. There are diehard shell fanatics, and I count myself as one of them, but today I wanted to mention the first GUI I really used: GEOS
I have fond memories of hooking it up to our color television and using the geoPaint program. It was fascinating at the time. These days we take the simple tasks for granted. Being able to draw, in color, on a computer was absolutely amazing. There were other programs available on GEOS, but I always was drawn
to geoPaint. Think about this an entire OS written and usable on a 5 1/4 diskette. If you have a few minutes read the Wikipedia article and then follow up with the link http://zimmers.net/geos/
Take some time and read through the FAQ and see what people were using back in the day.