Agora
   OO prototype-based, reflective language, based on only message passing, a key trait of OO languages; it allows late-binding polymorphism, the key trait making possible incremental modifying of programs. Descriptions, papers, implementations: Smalltalk, C+
   http://prog.vub.ac.be/research/agora/

Brain
   High-level, pure object-oriented, prototype-based, scripting language; Smalltalk-like syntax; some features borrowed from Scheme, Self, JavaScript. [Open Source, LGPL]
   http://brain.sourceforge.net/

Isaac Project
   Small prototype-based high-level language, influences: Smalltalk (all values are objects), Self (prototypes), Eiffel (Design by Contract); allows system, low-level programming, compiler has means for late binding suppression, optimizing type predictions a
   http://isaacos.loria.fr/li.html

MLud
   A runtime-extensible language built on top of SML/NJ designed for building collaborative environments. Supports dynamic delegation with multiple dispatch, several useful datatypes, inline ML, and checkpoint persistence.
   http://moonflare.com/code/mlud/

OScheme
   Small, embeddable interpreter, mostly Scheme R4RS conformant, with extensions: supports prototype-based object model, some POSIX system calls, compilable in secure mode.
   http://koala.ilog.fr/abaird/oscheme/oscheme.html

Object-based PLs
   By Rainer Blome. Alphabetized list with descriptions of, and links to, many prototype-based languages.
   http://www.pasteur.fr/~letondal/object-based.html

Prototype-based Programming
   Growing article, with links to many related topics. [Wikipedia]
   http://en.wikipedia.org/wiki/Prototype-based_programming

Slate
   Language-OS based on CLOS, Self, Smalltalk; Smalltalk syntax; libraries inspired by Common Lisp, Dylan, Strongtalk (strong typing). Descriptions, programming manual, tutorials, summaries, bulletin board Swiki, CVS. [Open Source, LGPL]
   http://slate.tunes.org/

The Slate Programming Language
   Brief description with many forum comments. [Slashdot]
   http://slashdot.org/developers/04/03/27/1627220.shtml