All 7,823 lines of the source code listing for the Fractal Engine 3 written in GFA BASIC 3
Many years ago I co-wrote, with Daniel Grace, a very complete Mandlebrot and Julia set explorer for the Atari ST.
This is the source code in GFA BASIC for version 3 of the Fractal Engine, which was published in issue 42 of ST Format
magazine.
The drawing engine code was written in 68000 assembler by Dan; so this is purely the application code. The 68000 assembly code has sadly been lost in that way that things get lost along the way in life.
It was one of the most complete software projects I've ever done, and I'm still really proud of the program we wrote. More information about it at http://mbharris.co.uk/fe3