Dynamo is an open-source visual programming application from Autodesk that aims to be accessible to non-programmers and programmers alike.
It gives users the ability to visually script behavior, define custom pieces of logic and run custom code segments using various textual programming languages.
Dynamo can be used as a standalone product (Sandbox) or can plug into other products such as Revit (Dynamo for Revit).
For more information on Dynamo please refer to the Dynamo Primer.