https://www.hpi.uni-potsdam.de/hirschfeld/trac/SqueakCommunityProjects/wiki/designer
Worked once, URL sarted not responding on 2021-04-11. May be temporary.
(Installer mc http: 'http://www.hpi.uni-potsdam.de/hirschfeld/squeaksource/')
   project: 'MetacelloRepository';
   install: 'ConfigurationOfDesigner'.
(Smalltalk at: #ConfigurationOfDesigner) load.
UiDesigner open
Up-to-date for Squeak 5.3, 2021-04-11
Morph subclass: #MyDialog
	instanceVariableNames: 'ui'
	classVariableNames: ''
	poolDictionaries: ''
	category: 'MyProject-Dialogs'
MyDialog>>ui
  ^ ui ifNil: [ui := MyDialogUi new]
MyDialog>>initialize
   super initialize.
   self ui setupUi: self.
   "other initialization here"
MyDialog>>open
   self openInWindowLabeled: 'My Dialog'.
Now access UI elements under self ui