Sketch, Affinity, Skala
Five years ago, when I would look for a vector design tool on the mac, there really didn't seem to be much. Illustrator has always felt very opaque to me, Inkscape's requirement on X made it mac-compatible, but felt very clumsy.
Lately, this seems to have become a hot zone for new tools. Sketch has obviously been "killing it", getting a lot of attention. Photoshop's designers seem to be doubling down on Photoshop as a tool for design. Skala has been "in progress" for long enough to attract attention, even though it's hard to form an opinon about something that's not yet released, and now Affinity Designer has entered Beta and looks to be a potential contender.
I haven't seen Skala, and I haven't used the Affinity Designer beta yet, so they may not truly be targeting the same niche. There's a distinct difference between a vector tool made for illustration and one made for design. Still, while I'm happy with Sketch, I am looking forward to increased competition and more choices, and I hope they're all great.