"Method Draw is a fork of SVG Edit, a web based SVG editor.
The purpose of Method Draw is to improve the usability and user experience of SVG Edit. It removes some features such as  
layers and line-caps/corners in exchange for a more simple and pleasant experience."

Dillinger is a cloud-enabled HTML5 Markdown editor, synced with Dropbox, GitHub, Drive (Google or MS)...

"This module replaces the command line editing experience in PowerShell.exe. It provides : syntax coloring, error notifications, multi-line experience, bash style completion, undo/redo, saving of history across sessions..."

"EpicEditor is an embeddable JavaScript Markdown editor with split fullscreen editing, live previewing, automatic draft saving, offline support, and more."

"At GitHub, we're building the text editor we've always wanted. A tool you can customize to do anything, but also use productively on the first day without ever touching a config file. Atom is modern, approachable, and hackable to the core. We can't wait to see what you build with it."

"Create word-processed text on the web using a reliable, fast and unbelievably beautiful editor."

"Sed (streams editor) isn't really a true text editor or text processor. Instead, it is used to filter text, i.e., it takes text input and performs some operation (or set of operations) on it and outputs the modified text. Sed is typically used for extracting part of a file using pattern matching or substituting multiple occurances of a string within a file."

Zen Coding : une nouvelle façon d'écrire son code HTML et CSS avec une syntaxe utilisant les sélecteurs CSS. Je n'avais pas vraiment compris avant de voir la démo, mais ça vaut le détour.
Zen est disponible pour de nombreux éditeurs : http://code.google.c