Dave Fischer Weblog

APL (AKA "A Programming Language") is a programming language that was popular in the 60s and 70s, and continues to be used in some obscure niches. It is notorious for being extremely dense and unreadable, and famous for being good at performing complex mathematical operations on arrays and matrices. The original versions used a custom character set of math & logic symbols, thus requiring a special terminal with an APL keyboard.

The Tek-4013 (storage-tube vector graphics terminal from the early 70s) had an APL mode, and both ASCII & APL characters on the keyboard.

(Also note the X/Y dials on the far right of the keyboard, which were used to position cross-hairs on the screen, like using a mouse.)