The Player Project creates Free Software that enables research in robot and sensor systems. The Player robot server is probably the most widely used robot control interface in the world, and supports a wide variety of hardware. Client libraries in C, C++, Python, and Ruby are officially supported, while Java, Ada, Octave, and others are supported by third parties. Its simulation backends, Stage and Gazebo, are also very widely used.
Released under the GNU General Public License, all code from the Player Project is free to use, distribute and modify. Gazebo is developed by an international team of robotics researchers and used at labs around the world.
Stage
Stage is a 2D multiple-robot simulator from the Player project. Stage simulates a population of mobile robots, sensors and objects in a two-dimensional bitmapped environment. Stage is designed to support research into multi-agent autonomous systems, so it provides fairly simple, computationally cheap models of lots of devices rather than attempting to emulate any device with great fidelity. We have found this to be a useful approach.
Gazebo
Gazebo is a 3D multiple robot simulator with dynamics from the Player project. Gazebo is a multi-robot simulator for outdoor environments. Like Stage, it is capable of simulating a population of robots, sensors and objects, but does so in a three-dimensional world. It generates both realistic sensor feedback and physically plausible interactions between objects (it includes an accurate simulation of rigid-body physics).