SLip - a Lisp system in JavaScript, for browsers
A Lisp for the browser that is starting to look a lot like a Common Lisp; and on top of which an Emacs is being built, FOR THE BROWSER!
A guide to building an interpreter for your own language.
One day.... one day.
It's a Forth. It's a Lisp. It's lambda calculus. It looks like fun and also something I'd never actually really use.