Maqetta - Maqetta is an open source project that provides WYSIWYG visual authoring of HTML5 user interfaces.
PageBreeze HTML Editor - A full-featured but easy to use visual (WYSIWYG) HTML editor for creating web pages. Includes a completely new editor with support for the latest HTML standards, many new formatting features, improved stability and ease of use.
Google Web Designer - Google Web Designer is a free, professional-grade HTML5 authoring tool. Build interactive, animated HTML5 creative, no coding necessary.
NSB/AppStudio - NS Basic/App Studio is a complete, powerful development environment.
BlueGriffon - An HTML editor based on Mozilla rendering engine.
Pinegrow - A professional visual editor for Bootstrap 4 and 3, Foundation, responsive design, HTML, and CSS. Convert HTML to WordPress themes.