HTML OnLive Debugger

jsFiddle lets one easily test snippets of JavaScript/CSS/HTML code on-the-fly, adding optional libraries like jQuery.

Liveweave is a HTML5, CSS3 & JavaScript playground for web developers and designers

CSSDesk is a online HTML/CSS sandbox. Experiment with CSS, see the results live, and share your code with others.

Tinkerbin lets you play around with HTML, JavaScript and CSS without creating files or uploading to servers.

An online playground with an instantly ready coding environment that supports several language preprocessors, CSS, HTML and JavaScript.

Test HTML / JavaScript / CSS snippets with real-time preview. You could also add libraries (jQuery, YUI etc.). Save your work with one click.

jQueryPad is a fast JavaScript and HTML editor. Just start it, enter the HTML you want to work with, bash in your jQuery code, and hit F5 to see the …

Online Interpreters in JavaScript. Online coding and REPL. Run and share code. Try QBasic, Forth, Ruby, Python, Lua, Scheme, Emoticon, Brainfuck, LOLCODE, Unlambda, Bloop, JavaScript, Javascript.next, Move,...

Compile and Execute your favorite programming languages online, click any of the following to proceed! Web Technologies, Text Formatting, Useful Utilities, Programming Languages. Vim, emacs modes are avaliable.

CodeBunk provides a Realtime Collaborative Editor with Compile/Run. CodeBunk is an Online Compiler/Interpreter for PHP, Python, Ruby, Perl, Lua, Javascript, C, C++. CodeBunk also has Peer-to-Peer Video/Audio...