I think you could say it was a niche in an existing broader market, which had previously been covered by Illustrator and Photoshop. Sketch came along with a foc

I think you could say it was a niche in an existing broader market, which had previously been covered by Illustrator and Photoshop. Sketch came along with a focused tool which did it better than the general-purpose tools. But it's not like UI protoyping was impossible before Sketch came along.