Stella

STELLA (short for Systems Thinking, Experimental Learning Laboratory with Animation; also marketed as iThink) is a visual programming language for system dynamics modeling introduced by Barry Richmond in 1985. The program, distributed by isee systems (formerly High Performance Systems) allows users to run models created as graphical representations of a system using four fundamental building blocks. STELLA has been used in academia as a teaching tool and has been utilized in a variety of research and business applications. The program has received positive reviews, being praised in particular for its ease of use and low cost. https://en.wikipedia.org/wiki/STELLA_(programming_language)

"business" version marketed as "iThink"