Tools that build themselves

My earlier post, It's the tools. Or is it?, reminded me what it is that draws me to certain software. Examples are TiddlyWiki, Emacs, and Tinderbox. All three of these are (mostly) self-contained systems within which one can take notes, manipulate them, and generate output using built-in facilities. Tinderbox is not a Quine, exactly, but it allows me to collect, write, and do all kinds of fancy things with text. Same with TiddlyWiki and Emacs. Their approaches are different, but it's a common thread that draws me to them.