UnoArduSim provides a virtual target Uno board and allows the user to choose, and interface to, one or more of several types of virtual input/output devices. 

Download UnoArduSim for FREE

Arduino Simulator 1.52 by Xervo (Windows & MacOS)

Free license key: 5FVKL-CMSM2-ZH9EX-UAFIX-AKRN9

Download Arduino Simulator

TinkerCAD – free, online 3D modeling program that runs in a web browser, and contains a Ardunio Simulator under “Circuits”

UnoArduSim & Ardunio Simulator – FREE