I used the Sketch "Delicious" free UI Kit for a food recipes app. It includes 11 pixel-perfect screens. I just added Proto.io interactions and created a great prototype! This Delicious UI Kit was designed by Robert Anitei Sketch source: https://www.sketchappsources.com/free-source/1765-delicious-ui-kit-sketch-freebie-resource.html

Using variables on a slider to control the Brightness and Hue of a light bulb

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A very basic Calendar example project using Containers a few states and 1 variable to track the year.

Graphics & Credit from: https://www.sketchappsources.com/free-source/3805-clean-web-login-form-sketch-freebie-resource.html. A simple Login page of a webpage using interactive Proto.io components.