Robot Operating System (ROS) is a collection of software frameworks for robot software development, (see also Robotics middleware) providing operating system-like functionality on a heterogeneous computer cluster. ROS provides standard operating system services such as hardware abstraction, low-level device control, implementation of commonly used functionality, message-passing between processes, and package management. Running sets of ROS-based processes are represented in a graph architecture where processing takes place in nodes that may receive, post and multiplex sensor, control, state, planning, actuator and other messages. Despite the importance of reactivity and low latency in robot control, ROS, itself, is not a Realtime OS, though it is possible to integrate ROS with realtime code.
Software in the ROS Ecosystem can be separated into three groups: (1) language- and platform-independent tools used for building and distributing ROS-based software; (2) ROS client library implementations such as roscpp, rospy, and roslisp; and (3) packages containing application-related code which uses one or more ROS client libraries. Both the language-independent tools and the main client libraries (C++, Python, and LISP) are released under the terms of the BSD license, and as such are open source software and free for both commercial and research use. The majority of other packages are licensed under a variety of open source licenses. These other packages implement commonly used functionality and applications such as hardware drivers, robot models, datatypes, planning, perception, simultaneous localization and mapping, simulation tools, and other algorithms.
ROS was originally developed in 2007 under the name switchyard by the Stanford Artificial Intelligence Laboratory in support of the Stanford AI Robot STAIR project. From 2008 until 2013, development was performed primarily at Willow Garage, a robotics research institute/incubator. During that time, researchers at more than twenty institutions collaborated with Willow Garage engineers in a federated development model.
In February 2013, ROS stewardship transitioned to the Open Source Robotics Foundation. In August 2013, a blog posting announced that Willow Garage would be absorbed by another company started by its founder, Suitable Technologies. The support responsibilities for the PR2 created by Willow Garage were also subsequently taken over by Clearpath Robotics.
ROS areas include:
A master coordination node
Publishing or subscribing to data streams: images, stereo, laser, control, actuator, contact ...
Node creation and destruction
Nodes are seamlessly distributed, allowing distributed operation over multi-core, multi-processor, GPUs and clusters
Husky A200 robot developed (and integrated into ROS) by Clearpath Robotics
PR1 personal robot developed in Ken Salisbury's lab at Stanford
PR2 personal robot being developed at Willow Garage
Raven II Surgical Robotic Research Platform 
rosbridge protocol and server Brown University developed the rosbridge protocol to enable any robot or computing environment to integrate with ROS using JSON-based messaging, such as for common web browsers, Matlab, Microsoft Windows, OS X, and embedded systems
Shadow Robot Hand – A Fully dexterous humanoid hand.
STAIR I and II robots developed in Andrew Ng's lab at Stanford
SummitXL: Mobile robot developed by Robotnik, an engineering company specialized in mobile robots, robotic arms and industrial solutions with ROS architecture.
UBR1 developed by Unbounded Robotics, a spin off of Willow Garage.
Roscopter is a ROS interface for ArduCopter using Mavlink 1.0 interface. roscopter gives data and information on IMU, GPS, RC Input, airspeed, groundspeed, heading, throttle, alt, climb states. It can also control airborne devices by passing RC values back to ArduCopter. Currently its only available for Hydro or lower version
^B. Hannaford, J. Rosen, Diana CW Friedman, H. King, P. Roan, L. Cheng, D. Glozman, J. Ma, S.N. Kosari, L. White, 'Raven-II: AN Open Platform for Surgical Robotics Research,' IEEE Transactions on Biomedical Engineering, vol. 60, pp. 954-959, April 2013.