Image via Fstoppers
These and a few others mentioned elsewhere:
Anthony Colangelo of Happy Cog reviews Sketch, on A List Apart
Jon Hicks uses Acorn and Sketch
Khoi Vinh on Sketch
Alternative apps to everything in Adobe Creative Cloud, on Mac.Appstorm
15+ alternatives to Adobe Creative Cloud, on Web Designer Depot
If you've used any alternatives it'd be great to know what you think.