I learned proraming on an Atari 520-ste. The language I had access to at the time was GFA basic.
I remember dumping the memory in binary to find where the mouse pointer was, and customize it. Yes, yes, it took a couple hours, but I found 2 memory blocks where the 0 and 1 drew the mouse pointer. I wrote my little program to change those 0s and 1s and voila! I had a totally original mouse pointer. It was the good old days...
You can still use GFA basic on PCs nowadays if you look around hard enough.