The few end user apps I have seen written in Squeak all use
SystemWindow for their top-level window. The result is one main window
with a Squeak-generated title bar inside the VM's main window - that's
wrong from a user's perspective.

I never could understand why Squeak developers do this. It's so easy
to get rid of SystemWindows.

Try this: In a fresh image, get the halo on the PluggableText in the
Welcome window. Take it out with the black handle. Then, get the halo
for the World, set its layout to proportional. Done. You have the
former SystemWindow contents filling the whole Squeak window. Adapts
to resizing, too.

- Bert -