Floobits brings real-time collaborative editing to text editors, IDEs. Collaborative text editors and screen sharing solutions usually suffer from the following problems:

Users are confined to looking at the same thing.
Only one user can edit at a time.
One person is usually stuck in an unfamiliar editor.
Only 2 people can work at a time.

We started building Floobits for ourselves to address these concerns. Floobits allows multiple users to simultaneously edit any file using the text editors they already know.

Interactive code to flowchart converter. Turn your workflows, algorithms and manuals into easy to understand diagrams via simple code.

The Monaco Editor is the code editor that powers VS Code.
Rich IntelliSense and Validation for TypeScript, JavaScript, CSS, LESS.
Basic Syntax Colorization for HTML, XML, PHP, C#, C++, Razor, Markdown, Diff, Java, VB, CoffeeScript, Handlebars, Batch, Jade, F#, Lua, Powershell, Python, SASS, R, Objective-C.

An HTML5 Presentation Editor. A GUI / Authoring Tool for ImpressJS and Bespoke.js
Source at https://github.com/tantaman/Strut

The simplest app for Bootstrap prototyping. Create quality HTML prototypes quickly, using popular open source tools like Bootstrap, LESS, Fontawesome and more. Work visually and with sources simultaneously, with no need to export. Easily integrates into developers' toolsets (Git, text editors, etc.) Works with plain HTML and LESS files. Generate only standard Bootstrap 3.3 HTML and LESS markup.

A better way to conduct remote interviews
WebRTC based video chat + code editor = Awesome interviews

an open source rich text editor based on HTML5 technology and the progressive-enhancement approach.

Diagramo is an online flowchart software.

Online code editor and playground.

Maqetta is an open source project that provides WYSIWYG visual authoring of HTML5 user interfaces. The Maqetta application itself is authored in HTML, and therefore runs in the browser without requiring additional plugins or downloads.

MobWrite converts forms and web applications into collaborative environments. Create a simple single-user system, add one line of JavaScript, and instantly get a collaborative system.

Powerful graphics editor for your web browser and pc

CKEditor is an open source WYSIWYG text editor designed to bring common word processor features directly to web pages, simplifying their content creation. Its core code is written in JavaScript.

Etherpad is an Open Source online editor providing collaborative editing in really real-time powered by Node.js

Snippely is a basic text and code organizational tool. Instead of storing bits of code, quick notes, and memos in text files all over your hard drive, this application will let you save and organize "snippets" in one convenient location.

WYSIWYG Content Editor, Inline Rich Text Application

DrawAble Markup Language

User friendly XML editing software

PSPad - code editor for developers for Microsoft Windows systems