Lego is described as '🚀 Web-components made lightweight. Future-proof'. There are more than 10 alternatives to Lego for a variety of platforms, including Mac, Windows, Linux, Online / Web-based and Self-Hosted solutions. The best alternative is Vue.js, which is both free and Open Source. Other great apps like Lego are React (Free, Open Source), AngularJS (Free, Open Source), Svelte (Free, Open Source) and Polymer (Free, Open Source).
Polymer is a library that uses the latest web technologies to let you create custom HTML elements. Build anything from a button to a complete application as an encapsulated, reusable element that works across desktop and mobile.
You can write less code with Ember's Handlebars integrated templates that update automatically when the underlying data changes. Ember.js incorporates common idioms so you can focus on the development of your application ( and not reinventing the wheel ).
Riot lets you build user interfaces with custom tags using simple and enjoyable syntax. It uses a virtual DOM similar to React but faster. Riot is very tiny compared to industry standards. We think there is a clear need for another UI library.