Stylo is an open-source web editor, design with app developers in mind.
- Element sizing/resizing;
- Shadow implementation;
- Copy&Paste (works even with objects in newer Chrome versions);
- Context menus;
- Color picker;
One feature I didn’t see addressed, though, was export capability; the app works offline, but wider export options would be much in place.
- Website: http://styloapp.com/