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++, Java, Scheme; MiniMix.
Class-based NewtonScript Programming
An article for PIE Developers magazine describing a technique for structuring a NewtonScript program using class-like objects.
Glyphic Script, Codeworks
Language with interactive development environment, supports multiple views per object, bytecode VM; was user programming environment of EO communicator; description, PDF manuals. By Mark Lentczner.
Was Poe: prototype inheritance language and OO virtual machine for building network-accessible programs for multiple programmers, users, agents. Persistence and garbage collection are automatic and transparent. [Open Source, GPL]
Growing article, with links to many related topics. [Wikipedia]
The Slate Programming Language
Brief description with many forum comments. [Slashdot]