I'm curious: the "Script" screenshot looks like it's using standard GEM Desktop, while the "Signum" is some other desktop. Are these both for ST? Was Signum written using some other full-screen graphic environment?

Signum! was highly opinionated. It ran on the Atari ST but did its own thing for the user interface. You could access a lower layer of drawing primitives and obviate GEM. In those days multitasking did not exist.

There were a good number of these kinds of application back then. Steve was one, GFA Basic another.