Designing a robot physically and validating it at every step is an arduous task. Contemporary robotics simulators can help to achieve laborious physics simulations, 3D visualizations, virtual robot modeling and novel research work that save time and money. Simulators are written in numerous programming languages like C, C++, Java, C# and other OOP languages that decide their platform compatibility. Some robot simulators use physics engines like ODE, Karma Engine for better simulation that include responses like collision detection, scene representation and rigid body simulations. Some use sophisticated 3D graphic aids like OpenGL and Graphic cards (NVidia, ATI) rather than traditional Direct3D, considering various facets like cost, portability and extensions. Codes can be transferred to the real robots from some simulators after proper verification for their operation. Unlimited features like multiplayer, controllers transference over networks, `special effects' and so forth, keep on pouring. This paper proffers some of the widespread commercial/ open-source simulators for robots and UAVs used in market. Further, I conclude that any kind of robot including legged, wheeled or UAVs can be simulated using simulators available in market with continuous endeavors to upgrade these simulators.