Gridlex is described as 'Simple. Robust. Responsive. Flexible' and is an app in the Development category. There are more than 25 alternatives to Gridlex for a variety of platforms, including Online / Web-based, Self-Hosted solutions, CSS, Mac and Windows. The best alternative is Bootstrap, which is both free and Open Source. Other great apps like Gridlex are Bulma (Free, Open Source), UIkit (Free, Open Source), Semantic UI (Free, Open Source) and Foundation (Free, Open Source).
Structure is a 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.)