I'm sure a lot of us could rip the real-time/live updating/auto-synchronizing (pick your term) engine out of our current web apps and package it up in a tiny framework without much effort.
We do things a little differently. We built SpaceMagic while working on a real-time web app of our own and did so with the goal of making our work as easy as possible. Ideally, we want to make developing realtime apps as easy as it is to make non-realtime apps. First, we support semantic HTML templates, allowing developers to turn their mocks into working prototype applications with a bit of javascript. Second, we make developers able to write validation and other important code once and have it run on both the client and the server. Third, SpaceMagic is released as just another npm package that works with your preexisting Node install and packages.