Harp is described as 'The static web server with built-in preprocessing' and is an app in the Development category. There are more than 50 alternatives to Harp for a variety of platforms, including Mac, Windows, Linux, Online / Web-based and Self-Hosted solutions. The best alternative is jQuery, which is both free and Open Source. Other great apps like Harp are AngularJS (Free, Open Source), GitHub Pages (Freemium), Neocities (Freemium, Open Source) and ExpressJS (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 ).