From Paterva Wiki
What Are Local Transforms?
Local Transforms are just that, transforms that run locally (the same PC that Maltego is running on). These are applications that when called will produce output which results in entities within your graph. They can be coded in practically anything as long as they stick to the specification.
Why would i want Local Transforms?
Local Transforms allow for you to integrate with almost anything that your PC can get to without the need for you to go through our servers.
What languages are supported for Local Transforms?
Almost any language is supported that can produce output to STDOUT. We prefer scripting languages such as Perl and Python, but the choice is up to you.
Where can i get the Specification from
View it online Online Specification
Get the .pdf [http://www.paterva.com/docs/localTransforms-SpecIII.pdf]