Wired Science has a great appreciation of Logo's 40th anniversary. I loved Logo when I was kid — so much more fun than learning BASIC and COBOL and FORTRAN! I even went to Logo Camp and designed a tank-game. Somewhere on my hard drive, I have a tarball of my old Logo code from 1980.
As I remember it, LOGO was a triangular turtle that roamed across the monochrome screen of an Apple II in my first grade classroom. Wherever he went, a line of ink would follow him — it came from a pen that was tied to his tail.
My digital friend simultaneously gave me an intuition for geometry and how to think like a computer programmer.
I would type FORWARD 50 and the turtle would move forward. When I gave the command RIGHT 90, he would turn sharply to the right. If I prefaced those two commands with REPEAT 4 and surrounded them with brackets, the turtle would draw a square.
(Photo credit: "Turtle Graphics Ramblings" from Logothings Wiki)