You could take a look at AllcountJS. It's actually not a admin UI tool but rather a framework for rapid business application development. It builds auto-generated UI (grids, forms, etc.) from domain model descriptions in JSON-like format. Provides built-in security and user management. Supports view customization and theming (see extending docs). If you're already using Express in your application you could integrate them to run in single Node.js instance.
