Roboschool provides new OpenAI Gym environments for controlling robots in simulation. Eight of these environments serve as free alternatives to pre-existing MuJoCo implementations, re-tuned to produce more realistic motion. We also include several new, challenging environments.
After we launched Gym, one issue we heard from many users was that the MuJoCo component required a paid license (though MuJoCo recently added free student licenses for personal and class work). Roboschool removes this constraint, letting everyone conduct research regardless of their budget. Roboschool is based on the Bullet Physics Engine, an open-source, permissively licensed physics library that has been used by other simulation software such as Gazebo and V-REP.
See also https://openai.com/blog/roboschool/