Which mathematical software product was originally developed as a programming language called 'X' at MIT in the late 1970s before evolving into the commercial product we know today?

The field of mathematics has been revolutionized by specialized software tools that help visualize, calculate, and model complex mathematical concepts. These products have transformed how mathematics is taught, learned, and applied in various industries. This trivia question focuses on the history of a groundbreaking mathematical software product that changed how professionals approach computational mathematics.

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MATLAB (originally 'MATrix LABoratory')
Mathematica (originally 'SMP' - Symbolic Manipulation Program)
Maple (originally 'Symbolic Computation Group Language')
SAS (originally 'Statistical Analysis System')