psx cms is an social content managment system written in php and based on the psx framework. The code is writte in clean php 5 oop and the backend is based on ExtJS. psx cms is a "social" content managment system because its also an OpenSocial API container and has other social technologies implemented like OAuth and OpenID.
psx cms has an extensive plugin system with that you can add many functionallities to your website like (news, forums etc...) so you can build a website wich has a corporated design. It produces great markup so that you can read a website in an screenreader without javascript or css. This website is also based on psx cms.
psx cms also helps to bootstrap social technologies by acting as an reference. So you can see how you could implement an opensocial container, OAuth service provider or OpenID consumer in an PHP web application.
If you have questions to psx cms you can sign in with an OpenID or if you havent one with your email address. You can also send an email to the mailinglist. By the way psx cms is of course open source and licensed under the GPLv3.