Apologies if this is a slight deviation from the main discussion, but I thought it would be worthwhile to highlight Gazebo and Ignition.
Both Gazebo and Ignition are general purpose robotic simulation tools and are completely open source under the Apache 2.0 license. Gazebo has been under development since 2002, and has been successfully used in a wide variety of applications in both the commercial and government domains. Ignition represents the latest development efforts by Open Robotics in the simulation space. A good analogy is: ROS2 is to ROS1 as Ignition is to Gazebo.
While not targeted directly for car simulation, I believe Ignition covers many of the needs listed in this thread. Here are some useful links for your reading enjoyment:
The most immediate use-case for Ignition is the SubT Challenge, which requires real-time (ideally faster than real-time) simulation of worlds that span multiple kilometers with dozen of UAVs and UGVs. To meet these needs we have implemented, and are continuing to make improvements to, distributed simulation.This in particular might be attractive to the autonomous car domain.
We are also using Ogre 2.1 with PBR rendering, QtQuick with a plug-in interface for graphical tools, and DART for physics.
I’d be happy to answer any questions in this thread or elsewhere.