These are some of the commonly asked for references referred to in Design Patterns and which are available on-line.

ET++
Includes papers and the program.

InterViews/Unidraw
Complete source available.

[HHMV92]

An Object Oriented Architecture for Constraint Based Graphical Editing.
Richard Helm, Tien Huynh, Kim Marriott, John Vlissides. Third Eurographics Workshop on Object-Oriented Graphics Champery, Switzerland. 1992

This paper presents an object-oriented architecture that integrates the graphical editing framework Unidraw, written in Unidraw, with QOCA, a powerful constraint solving toolkit.

[Joh92]

Documenting Frameworks Using Patterns
Ralph Johnson. Proc of OOPSLA '92, Vancouver, BC, Canada. (PostScript 342k)

[Choices]

Many references to the Choices object-oriented operating system.

[WG94]

ET++ - a Portable, Homogenous Class Library and Application Framework .
Andre Weinand, Erich Gamma.1994