A virtualization system implemented within a cloud server enables the simulation of robot structure and behavior in a virtual environment. The simulated robots are controlled by clients remote from the cloud server, enabling human operators or autonomous robot control programs running on the clients to control the movement and behavior of the simulated robots within the virtual environment. Data describing interactions between robots, the virtual environment, and objects can be recorded for use in future robot design. The virtualization system can include robot templates, enabling users to quickly select and customize a robot to be simulated, and further enabling users to update and re-customize the robot in real-time during the simulation. The virtualization system can re-simulate a portion of the robot simulation when an intervention by a human operator is detected, positioning robots, people, and objects within the virtual environment based on the detected intervention.