On the HHVM.com blog, there's a post talking about the speed of the HipHop VM (from Facebook) but how it still doesn't support everything built into PHP (and the work being done to bring it up to parity).

HHVM is a highly performant PHP runtime. In fact, it is nearly 40% faster than HPHPc, and only getting faster. [...] Performance is critical, but it isn’t everything. In order to gain broader adoption for HHVM, being able to run popular frameworks is a must; in other words, we can have the highest performing PHP runtime, but if doesn’t run real-world code without a lot of pain, then it won’t be used widely. Understanding this, we are putting serious resources around parity with the PHP runtime.

The post includes a table of features that have been ported and ones currently in the works, based on unit test coverage. They've based it on various well known PHP projects including PHPUnit, Symfony, Laravel, the Facebook SDK and many others. Their initial goal is to allow these frameworks to work 100% of the time inside the HHVM, but to continue the work from there, implementing other PHP features. If you'd like to help out with the process, they also welcome contributions.

In his previous post Allan MacGregor introduced the HipHop Virtual Machine (HHVM) and some of the functionality it offers. In this second part of the series sharing some "first steps" towards getting it running.

On a previous post "Introduction to HHVM" has no title attribute. we went over HHVM its history and the potential of running our PHP applications on top of it. Currently a few applications are fully supported like wordpress and drupal; more complex applications like Magento are still not 100% with HHVM due to bugs in the HHVM implementation. The first thing that we need to in order to start developing with HHVM is to setup a proper environment, for this case we are going to use a Vagrant Box.

He shows the steps to follow to get Vagrant up and working on your system (assuming you already have VirtualBox installed) and a base Ubuntu instance installed. Once its created and configured, then you can ssh into it and use apt-get to install all needed packages. There's a little bit of work you'll need to do to get ready for compiling the HHVM, but then you can clone the repository and run the build.