Inside the terminal, I could use the command 'explorer .' in Win32 or 'open .' in Mac to open GUI explorer/Finder.
What's the equivalent command in Ubuntu?
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xdg-open . will do what you want based on what is set as the default file manager, however since nautilus is the default I personally find it easier to autocomplete
(Note that xdg-open is supposed to supercede gnome-open, as it's a Freedesktop.org solution that is cross-desktop and agreed upon instead of GNOME/KDE specific)
You may wish to give a chance to dolphin, which can be easily installed (if not already) by dropping the next line in a terminal:
sudo apt-get install dolphin
Dolphin is more like a "Finder" and it features the sliding effect in the vertical columns when opening folders and some other useful features.
After installind (or if already installed) drop the next in a terminal, or [Alt][F2] in order to invoke the "Run application" box in order to enter the next command:
A screenshot is placed here for you to see dolphin in action.