It looks as though some initial write-up was deleted.

Forth is a programming language that was created in 1970 by Charles Moore. One of the things that make it interesting is that Forth combines the functions of operating system and programming language. It is a stack-based language: most, if not all, commands manipulate the stacks in some way. Forth uses two stacks: a data stack and a return stack. It is also possible to temporarily store data on the return stack.

Because it is stack based, Forth's commands are postfix (Reverse Polish Notation). For example,

(a + b) / c
would be written in Forth as
a b + c /
One of the points of writing commands in this way is that it is optimized for the computer: this is how the computer would do it anyway: it pushes the operands onto the stack and then executes the function.

It might seem that a language that consists of such primitive functions would be difficult to work with. On the contrary, development time in Forth is very fast and relatively bug-free, as compared with other languages. The reason being, that it is easy to declare "words" in Forth that encapsulate functionality. To put it another way, Forth programmers create a new language each time they write a program. (Scheme and Lisp enthusiasts should recognize this rationale.)

Forth is still very much alive and is found, for example, on every Sun microcomputer in the Open Boot PROM.