Are there any UI's that you find incredible, either from an artistic or technological perspective, and what is it about them that captures your attention?
While it doesn't replace Excel fully, you can use it and almost forget you're using a "webapp." The cells/columns look great, feel great, and they almost nail the desktop experience down to a tee.
It is actually a fairly old webapp, but I still haven't seen anything which made you forget that it was a webapp quite that well. Even GMail/Outlook.com still feel like webapps even with how good they both are design wise.
In the 10ish years that I've been using software I don't feel it has really improved much. I think my ideal UI is a traditional window with a few menu items and a really deep preferences window, like some of the software I used to use on OS X Leopard. Lots of recent software seems to sacrifice customisability in the name of simplicity (Windows 8+, GNOME 3, Ubuntu Unity). I don't think this needs to be the case, complexity tucked away inside menus won't ever bother users who want pure simplicity. I think lots of developers drawn to the "command-line-only" mindset would actually be happier with GUIs of this kind, but I'm speaking only from my experience (I use the command-line extensively, and Linux, not OS X).
The reset mechanism for an hourglass is intuitive and gives very clear feedback on whether or not the operation suceeded
I think that’s why SL is still so popular because it got the interface right, non-technically inclined people can learn to build rudimentary objects in a couple hours and its enough to hook many of them into becoming content builders.
Another would be FoxBase+/Mac for under a meg of object code the UI for data management and screen/form building was great. I got ugly when MS came in and standardized it into FoxPro for Windows compatibility.
The oldest best UI was the Print Shop on 8-bits changed the face of cork bulletin boards since.
Also I remember being pretty blown away when Delphi came out.
It's UI's are sufficient for the spectrum of users, not tailored as demoware or onboarding new users You can even awk and sed the drawing data.
Touchscreen-centric gadgets have appeared long before the iPhone came to the market, but the work Apple put in to the first iPhone's UI made touchscreens more useful than the traditional phone keypad interface for the first time.