Just when you thought two UI concepts (one for the desktop, one for tablets) were enough, here comes a third one: Zest UI, for smartphones. (Zest means both “the outer peel of a citrus fruit used for flavoring” and “enthusiasm”. )
I also updated the two other UI concepts. I plan to talk about the changes soon (although, as always, that depends on whether I have the time and energy).
On a less related note, here is an interesting source for GNOME mockups, along with all the Adwaita UI elements in theming/widgets: https://github.com/gnome-design-team/gnome-mockups (click on the “Zip” button to download the zip file). I sometimes use portions (like the Gnome Shell bar) for my mockups. I thought I mentioned it before, but looking through the archive, it seems I didn’t.