I definitely second this. You know Tk/Tcl isn't super flashy, but it certainly is snappy and gets work done well. Especially with add-ons like ttk, it's possible to build very sophisticated GUIs and sizable applications. It may not look like a shiny hipster application, but you can still build _quick_ applications with good UX that run on systems that are not overflowing with resources.

Really I'm still amazed people write Tkinter off as quickly as they do, and like to run it down, as it's often more performant, more available (it's pretty much everywhere), and more Pythonic than other choices, and works great when you're not trying to win a hipster design contest.

I don't know about other platforms, but on most modern systems, doesn't it just take on the current GTK+ theme? python/tk apps seem find to me most of the time.