What are some alternatives?
When comparing Gem.js and ember.js, you can also consider the following products
AngularJS - AngularJS lets you extend HTML vocabulary for your application. The resulting environment is extraordinarily expressive, readable, and quick to develop.
Vue.js - Reactive Components for Modern Web Interfaces
Backbone.js - Give your JS App some Backbone with Models, Views, Collections, and Events
Svelte - Cybernetically enhanced web apps
ExpressJS - Sinatra inspired web development framework for node.js -- insanely fast, flexible, and simple