EazyCSS - No code CSS editor for any website.
UMLGraph - UMLGraph is a professional automated drawing tool that allows the designers the declarative specification and drawing of UML class and sequence diagram.
Hoverify - All-in-one browser extension to improve your web dev experience.
draw.io - Online diagramming application
Devsync - Visually edit CSS. Live-sync the result with your editor.
yEd - yEd is a free desktop application to quickly create, import, edit, and automatically arrange diagrams. It runs on Windows, Mac OS X, and Unix/Linux.