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!
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.
A programmer's editor written in Common Lisp, written for Common Lisp, which aims to be a good Common Lisp IDE; but which also works as an IDE for other languages too.
Think Emacs in Common Lisp.