Nuke allows artists and technical directors to create gizmos, which are simply groups of Nuke nodes that may be reused by other artists. These are equivalent to Shake’s macros. Studios commonly use gizmos to consistently apply certain color grading techniques, process incoming footage according to a particular conversion formula, and process outgoing footage in preparation for film printing.
A gizmo is a Group Node that you create and save in a separate .gizmo file in your Nuke plug-in folder. Nuke scripts can use this gizmo just like any other node type. Saved scripts only contain the name and control settings for the gizmo; the definition is in the gizmo file and it is read at the same time the script is loaded into Nuke. Thus, you can alter the implementation of the gizmo and change all the scripts that are using it.
NOTE: Unlike other nodes, gizmos cannot be cloned.