UnoArduSim is described as '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'. There are three alternatives to UnoArduSim for a variety of platforms, including Windows, Linux, Mac, Online / Web-based and Self-Hosted solutions. The best alternative is Autodesk Tinkercad. It's not free, so if you're looking for a free alternative, you could try Wokwi Arduino Simulator or avr8js.
Tinkercad is a super easy-to-use, browser based 3D design tool. With Tinkercad you can create 3D printable items: toys to play with, decoration to light up your home or jewelry to express yourself. You dream it, you can make it!
The app is used to draw circuits as well as simulate the Arduino Code right in the browser. Wokwi Arduino simulator creates diagrams as well as actually runs tie application code on the AVR8js platform.