TweetCoding (<=140 chars of AS3)

"Visualizing a Recursive Execution Stack", by @gskinner, in 139 characters
Flash CS4 with strict mode turned off required to compile.

x=275;y=400;with(graphics){(function f(x,y,m,d){lineStyle(d,0,1);lineTo(x+=d*6*m,y-=40);if(--d<0)return;f(x,y,1,d);f(x,y,-1,d);})(0,0,0,9)}