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

A project which simulates a collision between 2 objects. Freely drag the objects onto each other in order to have their core color change when colliding.

A halloween project i have put together using the Proto.io Halloween icon set: https://proto.io/freebies/free-halloween-icons/