CodeDesigner is a free open-source RAD tool that will help you create different diagrams for creating application form and logic as well as creating source code for production.
The program allows you to create UML Diagrams, Symbol State Diagrams and Hyperlink State Diagrams.
It supports ANSI C, C ++ and Python languages. If you add enough details, the program can create code for applications outside the diagram.
It is a free alternative to commercial equipment like Enterprise Architect or IAR Visualist.