Ambrai Smalltalk is an implementation of the Smalltalk language and development environment for Mac OS X. They are currently offering free time-limited betas for download

This page and its linked pages describe Icicles, which provides extensions to ‘completing-read’, ‘read-file-name’, and ‘M-x’. Most of these extensions involve minibuffer input completion and cycling.

SCPlugin allows access to Subversion commands from the Finder