Jelix is an open-source framework for PHP5.
It has a modular, extensible architecture. Applications based on Jelix are made with modules, which allow to reuse features in several projects.
For more informations, read http://jelix.org/articles/en/features
Sources in the repository are not useable directly. You must "build" jelix. But it's certainly better for you to download a package containing Jelix ready to use. See the download page.
Jelix 1.5+ is compatible only with PHP 5.3 or more.
Read the first chapter of the manual to install Jelix and to create an application
You have a full manual to learn Jelix. You can read it direcly on the website, or you can download the PDF edition.
You can ask your questions on the forum or on our IRC Channel, #jelix, on the irc.freenode.net network.