I included some links to other ideas here: https://news.ycombinator.com/item?id=7755759 and here: https://news.ycombinator.com/item?id=7756215 and of course here is some stuff about Morphic: https://en.wikipedia.org/wiki/Morphic_(software) -- but the important point is that there are so many ways of doing things, that there's no way to summarize them all!

But taking a few steps back from which three letter acronyms to use:

User interface software architecture is so dogmatic and cargo cultic these days, compared to how wide open and free wheeling it was years ago when nobody agreed on anything, and people were experimenting with building all kinds of uniquely original systems from the ground up, instead of iterating on imitating imitations of imitations like they are today.

One book that deeply impressed and influenced me, and made me realize how many extremely different approaches and ways of thinking about user interfaces there were, was "Methodology of Window Management", the proceedings of a 1985 workshop where an amazing group of brilliant pioneers got together and discussed a wide range of vastly different approaches and ways of thinking about user interface architecture and software design. Fortunately it's online now and you can read it for free!

http://www.chilton-computing.org.uk/inf/literature/books/wm/...

Overview

F R A Hopgood, D A Duce, E V C Fielding, K Robinson, A S Williams.
29 April 1985.
This is the Proceedings of the Alvey Workshop at Cosener's House, Abingdon that took place from 29 April 1985 until 1 May 1985. It was input into the planning for the MMI part of the Alvey Programme.
The Proceedings were later published by Springer-Verlag in 1986.

It's got some great historical retrospectives, like Warren Teitelman's "Ten Years of Window Systems - A Retrospective View", describing much of the groundbreaking work at Xerox PARC: http://www.chilton-computing.org.uk/inf/literature/books/wm/... -- and some papers about cutting edge technology of the time, like James Gosling's "SunDew - A Distributed and Extensible Window System", which was the original name of NeWS: http://www.chilton-computing.org.uk/inf/literature/books/wm/... .

For example, AJAX was not invented in 2005 -- that's just a recent buzzword for a much older good idea:

http://www.chilton-computing.org.uk/inf/literature/books/wm/...

"There was a general view that the ability to download procedures to the window manager was a good way to tailor facilities to applications, for example to filter out all mouse events for a particular application. The same effects can be obtained through table-driven systems, though downloading was felt to be more elegant. However, there is still more work to be done in this area."

Even though some of the information may seem dated and laughable, like the "Interface to GKS": http://www.chilton-computing.org.uk/inf/literature/books/wm/... -- it's still valuable and amusing reading, just to get the perspective that people haven't always agreed on basic concepts like what an icon is, or what you can do with a window, and that there is still a lot of room to innovate if only we stop rehashing old ideas. The back-and-forth in the working group discussions is fascinating and prescient, and I think it's even more interesting to read today than it was before, to compare their predictions and recommendations with what's evolved over the 29 years since it was published.

http://www.chilton-computing.org.uk/inf/literature/books/wm/...

"18.8.4 Icons.
Icons are regular (small) pictograms which may be defined and changed by applications. They can serve many functions, frequently to conserve screen real estate. They can be used as an alternative to a window as in Cedar; as an alternative representation (perhaps concurrently visible) of the window (Sapphire); or as a representation of a task to be invoked or data which is to be operated on (STAR, Macintosh). The icon can thus range from an application-prescribed static bitmap representation to an entity which has all the attributes of a window (eg can receive all types of input). Since use of icons in user interfaces is commonplace. the provision of support in the window manager for operations on them is desirable."