HTMLPen is a free online Visual HTML Editor (WYSIWYG Editor) program allows you visually edit, preview, and run your html code. It is also a powerful online text editor.
A front end web development playground.
CSSDesk is a online HTML/CSS sandbox.
dabblet is an interactive playground for quickly testing snippets of CSS and HTML code.
Sample of the bin:
Plunker is an online community for creating, collaborating on and sharing your web development ideas.