At Sun we experimented with implementing an X11 window manager in NeWS. We didn't have transparency at the time (1992), but we did support shaped windows!
The NeWS window manager supported cool stuff (for both X11 and NeWS windows!) like rooms, virtual scrolling desktops, tabbed windows, pie menus, was easily extensible and deeply customisable in PostScript, and ran locally in the window server so it could respond instantly to input events, lock the input queue and provide feedback and manipulate windows immediately without causing any context switches or dealing with asynchronous locking, unlocking and event handling. You'd never lose a keystroke or click when switching between applications, for example.
I touched on some of those ideas in this ancient window manager flamey-poo:
http://www.art.net/~hopkins/Don/unix-haters/x-windows/i39l.h...
Also on that topic (I can't believe I still love flaming about this stuff so many years later! Sorry if I sound like a broken record.):
https://news.ycombinator.com/item?id=5861229
https://news.ycombinator.com/item?id=5844345
https://news.ycombinator.com/item?id=8039156
https://news.ycombinator.com/item?id=13198492
https://news.ycombinator.com/item?id=11520680
https://news.ycombinator.com/item?id=11319498
https://news.ycombinator.com/item?id=11319783
https://news.ycombinator.com/item?id=9977226
https://news.ycombinator.com/item?id=13196983
https://news.ycombinator.com/item?id=11481604
And here's how I think you should design a programmable "window manager" these days -- but it would be much more than just a window manager! It would be great for integrating legacy desktop and mobile applications into VR, for example!
aQuery -- Like jQuery for Accessibility
http://donhopkins.com/mediawiki/index.php/AQuery
Don asks Peter Korn: Hey I would love to bounce an idea off of you! I didn't realize how much work you've done in accessibility.
There is a window manager for the Mac called Slate, that is extensible in JavaScript -- it makes a hidden WebView and uses its JS interpreter by extending it with some interfaces to the app to do window management, using the Mac Accessibility API.
So I wanted to make pie menus for it, and thought of a good approach: make the hidden WebView not so hidden, but in the topmost layer of windows, covering all the screens, with a transparent background, that shows the desktop through anywhere you don't draw html.
Then just make pie menus with JavaScript, which I've done. Works like a charm!
THEN the next step I would like to do is this:
aQuery -- like jQuery, but for selecting, querying and manipulating Mac app user interfaces via the Accessibility framework and protocols.
So you can write jQuery-like selectors that search for and select Accessibility objects, and then it provides a convenient high level API for doing all kinds of stuff with them. So you can write higher level plugin widgets with aQuery that use HTML with jQuery, or even other types of user interfaces like voice recognition/synthesis, video tracking, augmented reality, web services, etc!
For example, I want to click on a window and it will dynamically configure jQuery Pie Menus with the commands in the menu of a live Mac app. Or make a hypercard-like user interface builder that lets people drag buttons or commands out of Mac apps into their own stacks, and make special purpose simplified guis for controlling and integrating Mac apps.
Does that sound crazy? I think it just might work! Implement the aQuery "selector engine" and heavy lifting in Objective C so that it runs really fast, and presents a nice high level useful interface to JavaScript.
Here is an issue I opened about it on the Slate github page, describing what I've done, but I haven't written up the "aQuery" idea yet. That's the next step!
http://www.donhopkins.com/home/archive/piemenu/uwm1/hacks.f
That's the FORTH source code from 1987 of a programmable multi threaded X10 window manager that lets you throw windows around so they bounce off of the edge of the screen!