I can't help but think of this line from "The Joy of Clojure"...

Go to any open source project hosting site, and perform a search for the term Lisp Interpreter. You'll likely get a cyclopean mountain of results from this seemingly innocuous term.

Lisp and Forth might be the only languages out there where writing a basic interpreter is a reasonable weekend project and a decent way to get your feet wet with some new language you want to learn.

Ok wow. Any few-weekends length resources you know about?