Compared to UML Activity Diagrams, DRAKON-Foo (where Foo can be Python, C, C++, Erlang, or any of a bunch of others):

(1) Is constrained in a way designed to enhance understanding of the visual flow, and

(2) Directly includes code (in language Foo) in the boxes, rather than text; that is, its a programming environment, not a diagramming language with text that gets converted to program code somewhere else that is maintained separately.

The first item is also a feature of DRAKON by itself.