Starlogo! I have fond memories of that... I can barely remember the instructions, but I can remember doing
Code:
create 1000
fd 1000
Which wouldn't lag the CPU down too much. Logo was what really got me into programming, because while everybody else was goofing off and playing Oregon Trail, I was making my turtles (they're not dots) do cool stuff. It's great for modeling cellular automata and live things in general, and also an excellent beginner's language, IMO.