I think some of the people that wanted to do this were thinking of the Cupo RocketDock skin by Guillen Design. There were also several other similar skins released at the time. When done properly, the look was quite effective.

I don't know that it would work for anything else though, other than an Ubuntu Style Sidebar that the OP was looking for.

Since the thread got so lively and there were quite a few replies, I guess I owe everybody one from my side.

First, I'm not going to pretend I know the difference between different UI elements. I guess you're right, Jorge, when you say that a dock is not supposed to behave like a taskbar. I guess I want a toolbar, or a sidebar, something that docks to the left side of the screen, and has some icons and applets in it. I now understand that Nexus is not supposed to be able to do this, since it's different in nature to the Ubuntu sidebar that I'm trying to mimic. Nevertheless, thanks for the understanding, and thanks for implementing the "stretch" feature in the application (I just read the message).

@nexter: I'm not a big fan of Ubuntu tbh, neither of Gnome (I don't dislike them, I simply don't feel either way about them). However, I think the idea of having a vertical toolbar that occupies space permanently is actually quite smart, given that most monitors (at least those that I use) are at least 16:9 and have much more horizontal real estate than vertical. But I still like the way the Mac dock (including the original Nexus look) looks and feels.

I did try to play around with shelves, a little, to see if I can get one to do what I want it to do. However, I opened the configuration file(s) for one of the skins and I was overwhelmed with the amount of options, so I simply gave up.

In the end, I did manage to create some kind of a Frankenstein combination of 3 overlapping docks, one using a heavily padded skin (both left and right) and the others not so much. The top dock has some launchers, the middle one contains only running apps, and the bottom dock contains some applets. The middle one overlaps the other 2 and is the only one that actually changes in size.

It looks quite nice TBH, but I suppose that there is room for improvement (I doubt that my creation is very tolerant to resolution changes), but this is the first iteration, the next one will be better, I guess. Screenshot attached.

...it's called and is the dock.

That's about as ugly as can be. :/

If there are more icons than screen edge, it simply scrolls, which is the optimal solution.

I knew the moment that I typed "Sidebar" that you would reply with the correct term. I was just too lazy to look it up.

I haven't used Ubuntu since version 15.10 or so. I believe it was called the Unity Launcher back then, although I remember seeing the term sidebar in some of the forums.

I did install Ubuntu on an early (2015) 13 inch MacBook Pro for a neighbor last year. It ran unbelievably fast. It automatically installed a printer connected to Wi-Fi, and worked flawlessly. It also looked very polished. It gave new life to a MacBook that had reached its end of life. I might give it a try again.

The Cupo RocketDock skin served no purpose other than changing the look. It was something different in a sea of skins. To quote a wise old moderator, "whatever floats your boat".

Beauty is in the eye of the beholder. I don't dislike it, for instance lol

Ah-ah! Caught you, you old purist, docks DO NOT scroll!

Nexus docks, for instance, will automatically reduce the icon size to fit (until a minimum of 16x16 at which point the dock simply gives up and lets you go beyond the screen edge if you are so keen on it lol).