Structure is described as 'Declarative, Flexbox based grid framework. Structure defines layout using non-standard attributes on elements. (If you have used frameworks like AngularJS, you have already gotten some exposure to declarative syntax and non-standard attributes' and is a CSS Framework in the development category. There are more than 25 alternatives to Structure for a variety of platforms, including Web-based, Self-Hosted, JavaScript, Vue.js and HTML5 Boilerplate apps. The best Structure alternative is Bootstrap, which is both free and Open Source. Other great apps like Structure are Tailwind CSS, Bulma, Semantic UI and Foundation.