Oberon OS Walkthrough (2009)
We used Oberon (the system and the language) in our 3rd year CS OS course in Stellenbosch in the mid 90's<p>Interesting system, it's worth looking at since it has a few unexplored ideas.<p>(I was less impressed the the language).<p>I experienced it at about the same time as win3 / Win95 and X-Windows (before KDE/Gnome) and it compared favourably.<p>I'm glad this post is calling attention to it, but I don't think the post does it much justice.<p>The Zooming-UI and desktops happened later as a reaction to (today) more mainstream approaches.<p>I wouldn't call the interface a CLI - it wasn't REPL.
It needed a 3 button mouse and was very point and click.<p>TUI is more accurate.<p>It was graphical, with no desktop and non-overlapping panels (although in certain cases one panel could obscure a lower panel). 
Think tiling window manager.<p>The mouse button use was chorded, so there were a lot of combinations, this meant one could highlight, select, copy, paste and execute commands without using the keyboard.<p>Any text could be selected and executed. Selecting 'Module.Function' would execute that function in that module.<p>It used a "Document Object Model", the base text class was expandable to handle more widgets than just native text.<p>Single user, single process with no real distinction between the system code and your own.
You could view and edit system modules and add your own.