macOS UI Kit
I recently got around to updating my Yosemite UI Kit.
It was ahem, a little out of date and since I did that originally, the whole designing in 1x or 2x debate has been settled and I had been planning on redoing the whole thing at 1x.
The new Sketch features (Symbol Overrides and Resizing Rules) were the decider for me.
I started from scratch and have given it a more appropriate name. Everything is designed at 1x as accurately as possible and of course entirely vector.
Most elements can be resized in expected directions and the symbol overrides make it easy to add icons to buttons, change text etc.