http://www.idupree.com/starplay/
This is a simulation somewhat like StarLogo (cf. Mitchel Resnick, Turtles, Termites, and Traffic Jams: Explorations in Massively Parallel Microworlds)
with "turtles" - active agents that move around the world using simple scripts,
and "patches" - a grid of locations that can hold state (and also do things if they want to).
The world wraps on the side and top/bottom (it's a torus).
The code I'm writing and playing with is in
playground/index.html and playground/playground.coffee.
This runs completely in-browser; presently you program it in CoffeeScript. There's an example starting script already visible in the browser that you can click on and edit. There are buttons in the top-right to re-compile and run the script; it will give you an error message if you have a syntax error. (Currently, the line number it gives you is not very usable, and various other things are probably tedious. It is not yet self-documenting.)
Tested in: current Firefox and Chromium.
It compiles to JavaScript and tries to have as straightforward a
correspondence between the CoffeeScript and the JavaScript
in order to aid debugging and make people more comfortable with
using CoffeeScript.
Indentation matters. The last line of a function implicitly
has a return prefixed to it if there isn't one there.
@ means this, and @thing means this.thing.
(a, b) -> stuff creates a function. Zero-argument functions
may have the argument tuple omitted (-> stuff).
Function-call argument parens, object-construction curly-brackets,
etc., may be omitted in some cases.
An entire CoffeeScript is wrapped in (function{...}()), and var
is implicit; thus it's impossible to write to global variables
except by saying things like window.foo = "bar".
Inspiration from StarLogo and many people.
Libraries Backbone.js, Underscore.js, jQuery, Raphaël, CoffeeScript (most of which I don't use currently)
Code started from Raphael demo "graffle" (though currently has nothing to do with it) http://raphaeljs.com/graffle.html