What are some alternatives?
When comparing Gem.js and Webix UI, you can also consider the following products
Vue.js - Reactive Components for Modern Web Interfaces
Kendo UI - Fast, light, complete: 70+ jQuery-based UI widgets in one powerful toolset
Svelte - Cybernetically enhanced web apps
Preact.js - Preact is a fast 3kB alternative to React with the same modern API. Components & Virtual DOM.