This plugin lets you use just your Webcam to estimate human figures similar to the XBox Kinect.

Plugin for using XBox controllers as an Input Device in Grasshopper

Fast GPU-based physics simulation in Grasshopper supports free particles, fluids, rigid bodies, soft bodies, cloth, inflatables and custom constraints

Zebra is a live multi agent behavior system(also known as Flocking or Swarming). Used to achieve design goals using agents.

Sculptured, organic modeling in 3D. SubD like interface, but advanced surfacing for high quality, geometrically rich shapes.

Box2D is a 2D rigid body simulation tool for Grasshopper. It uses Box2D physics engine and a C# wrapper from colgreen/box2Dx. 

PhysX.GH is a rigid body simulation tool for Grasshopper, using open source real-time physics engine NVIDIA PhysX.

Tetris Game for Rhinoceros.   Use Left/Right keys to move the block, Up key or Space key to rotate, and Down key to move it down.