well it's a bit old school but it certainly looks functional. If the program under it is good, it's a very superficial comment. If only you'd see my emacs screen, it's unbelievably ugly and somehow, I work with it every day !
For me, "non-ugly" means that it uses the standard UI controls and UI theme for the platform in a reasonable way. That's exactly what the screenshot shows. I would describe it as "neat". All your links are the exact opposite of that.
I'm sure someone (and, in particular, their designers) think they look nice. But the thing about looks is that they're very subjective. However, if I'm using some OS/desktop combo, that means I find its UI, at the very least, acceptable. And thus any app that uses native UI look & feel on that platform is also acceptable. I can't say that for many custom-themed apps.
For example, out of your links, I would say that 2 are downright ugly, and the third is tolerable. And I'm not sure what "in 2018" has to do with that.
