Probo is an open source continuous integration and quality assurance tool that lets you build branches and pull requests inside docker containers, reports back on the progress of each step, and then keeps the environment around and gives you a link so that you can go and preview the work in a shared space.
See the Quickstart guide for how to get up and running with your own instance of Probo
The code uses generators and requires node io.js or node 4.x+.