Marionette is the proprietary software developed and used in-house by Pixar Animation Studios in the animation of their movies and shorts. Marionette is not available for sale and is only used by Pixar. As a result, little is known outside of Pixar about the detailed workings of this software.
Pixar claims that Marionette is designed to be intuitive and familiar to animators who have traditional cel animation experience.
Pixar chooses to use a proprietary system in lieu of the commercial products available and used by other companies because it can edit the software code to meet their needs. One example of this editing is shown in extra features of The Incredibles DVD; it is explained that previous versions of Marionette were not able to stretch models in the ways needed to correctly animate Elastigirl so the in-house Marionette development team created a new version that included this feature.
The Marionette credit included with all Pixar films created on the system.