It's amazing to me the things that people share freely with the world, even though their efforts and genius are worth a great deal more than things people happily charge (and pay) for!
Latest in this ever-growing list is this open source Arduino emulator that runs right in your web browser:
https://github.com/lrusso/ArduinoSimulator?tab=readme-ov-file
Currently it emulates three different size of Arduino, plus the serial monitor, GPIO, and a development version of the EEPROM simulation.
It's very cool!
It's not the only one out there but it works very well and is not tied to any commercial code unlike some of the other projects.
Of course the big guys like Tinkercad and Wokwi have the advantage of not only emulating the base silicon but all the add-ons and widgets which make for full project capability rather than just executing code.
The core elements of the Wokwi code are open source, along with a lot of widgets, and people have done some fun things with it, starting with the obvious "blink" sketches.
And even RGB LED matrix demos
There is another advantage the full Wokwi has, and that is the ability to emulate not just the 8 bit AVR family but powerful, wifi enabled micro controllers such as the Pico W!
https://wokwi.com/projects/new/pi-pico-w
Can you imagine if they added an SD card simulation to this? We could have whole operating systems emulated on an emulated micro controller running in a web browser ;)