1. The right side buttons for edit, layout, etc. have tooltips (that's great) but they should be like on/off buttons e.g. clicking layout once puts the editor in layout mode, clicking it again should bring editor out of layout mode back into preview.
2. In Edit mode the buttons on the bottom work like on/off buttons (that's great) those buttons should have tooltips.
3. Editing an image I can't put an alt value or title? How accessible is the content created by the editor?
Keep up the good work. I would use this for quick website/blog setup.