Many PC users first encountered Lisp in the form of XLisp, an extended "object oriented" version of Scheme created by David Betz.
This contains the Medley virtual machine for a number of Unix -like systems.
librep is an Emacs Lisp-like runtime library for Unix. It contains a LISP interpreter, byte-code compiler and virtual machine. Applications may use the LISP interpreter as an extension language, or it may be used for standalone scripts.
Web-based application environment using a custom version of Lisp
A somewhat Scheme-like Lisp, designed by a group of European industrial and academic Lisp users and implementors. Bigger than Scheme, smaller than Common Lisp.
A public domain implementation of EuLisp
The critical notation provided by Lisp, a text-based data structure for representing complex data.
A small Lisp interpreter based on the Standard Lisp Report (1979) that implements garbage collection via the much-denigrated method of reference counting. It is intended to answer the question "Reference counting is slow, but HOW slow?"
... Suggesting why dynamic binding may not be so bad after all; the basic idea is that it aids extensibility.
If all you have is lexical scoping, then all values that are to be worked with by a set of functions must be named and explicitly passed from function to function. The result is that if one of the functions' data structures are extended, all of the functions potentially need to be modified to be able to get the data to where it is used.
With dynamic scope, the bindings stick around so long as they are referenced, and thus don't need to clutter up the argument lists of functions that don't use the values anyways.
If this scares you, then perhaps you're not ready to write extensible code...
This book implements a rudimentary Lisp that looks rather like a very early minimal Common Lisp in C.
Website for Goo Lisp system
GOO is a new type-based prefix syntaxed language that is simple, powerful and extensible. GOO is an acronym for Generic Object Orientator.
Nisp - a strongly-typed Lisp dialect
Logo was created as a sort of "Lisp for education."
This is a Lisp that is a little like a "pre-Common Lisp, pre-Scheme" Lisp. It may be interpreted or, with full type specifications, transformed into C that is then automagically compiled.
The ISLISP programming language is a small, standardized specification for a Lisp language, named ISO/IEC 13816:1997.
A full ISLISP implementation.
A language with Lisp syntax, Objective C object model.
Hyperpolyglot - a side-by-side reference sheet indicating comparative functions/features of Common Lisp, Scheme, Emacs Lisp, and Clojure. Seems pretty useful.
A simplified Clojure-like Lisp implemented in PHP