What's with the influx of Atari ST postings lately? I'm surely enjoying it!
Can EstyJS run in monochrome (640 x 400) mode? There were some great games in b&w, like Bolo and Oxyd [0] by Meinolf Amekudzi.
I remember studying the 'Hitchhikers Guide to the BIOS' [1], which was the only piece of documentation I initially had for the ST when it had just come out. If I'm not mistaken, it did ship with a C compiler and assembler.