Been working on a really awesome #cpp library for creating cross platform apps using any windowing protocol you want (Win32, UWP, Cocoa, UIKit, XCB, XLib, Mir, Wayland, WebAssembly) for quickly getting apps off the ground:

https://github.com/alaingalvan/CrossWindow

Still a WIP but it's coming along really well, with sister libraries to help create apps using any graphics API, and cross window, cross graphics API demos working. <3