PICSimLab is a realtime emulator for PIC, Arduino, STM32, ESP32, ...
Integrated Development Environment (IDE) for learning HDL
Allows you to build your own circuits and test them
A framework for implementing real-time control systems
Johnny - A Simulator of a Simple von-Neumann Computer
Virtual Simulator for Dynamical Systems
Rubik's Cube 3x3x3 Algorithms Simulator
Science simulator and advanced calculator based on modules