What language has two stacks? What language is used on satellites and in home computers? What language deals in words? Why, Forth, of course! Forth is a highly unique language developed in the 60s by Chuck Moore. And when I say unique, I mean unique. Forth uses reverse polish notation for all operations, along with a dedicated data stack for passing parameters. But it's not just unique for the fun of it, Forth's design is highly deliberate. It offers a level of simplicity and power that's rarely seen in programming languages. Selected Sources:
http://www.forth.org/POL.pdf - Moore's Programming a Problem Oriented Language
https://www.1strecon.org/downloads/Forth_Resources/CM_ForthLanguageInteractiveComputing_1970.pdf - Early paper discussing Forth
https://archive.org/details/1985-10-dr-dobbs-journal/page/41/mode/1up - Dobb's Journal article on the NX4000