Satis allows you to require private php packages in your projects. One of it's authors is Jordi Boggiano of composer/packagist fame. Over at the excellent Laravelista blog Mario Bašić explains how to install and use it.

I was working on three projects at the same time and I've found myself copying code from one project to another and then making small changes. And then I recognized a pattern. ... I created a package and as soon as it was ready for GitHub I remembered: "I can't open source this...". The package contained few paid html templates, company logo's, slogans, specific company text etc. ... This post will explain what Satis is, when to use it and how to set it up on your server.