In last month's 2015 DARPA Robotics Challenge (DRC), 18 of the 23 teams who competed used the open source Robotic Operating System (ROS), and 14 used an open source robot simulator called Gazebo.
Brian Gerkey, CEO of the Open Source Robotics Foundation noted that simulators like Gazebo "broadens access to robotics, which are inherently expensive. The lowest cost robot is one that exists in your computer." He added that unlike the PC market, where Windows came to market long before Linux, "in the case of robotics, open source got there first. The community grew up doing things the open source way."