I was reading up on LISP, and realized it would be pretty easy to implement my own parser and interpreter, so I did it. I created it in such a way that it is easy to expand in the future, so that I can use it for various projects that I'd like to use it for... game AI programming, Genetic Programming, and so on.
The approach I used for its architecture lets you implement both in-language functions, as well as external functions. This allows you to directly add in non-planned implementations of things like graphics libraries, like is done with podzilla, or Smart Painter, as well as for other hardware interfaces and the like.
It was written to have a very small code footprint. It was coded using the NoWeb literate programming method, so everything was very well documented.