Here are top 10 free PHP CMS collected from many sources (not sorted on rankings)
1. Drupal
download: http://drupal.org/project/Drupal+project
demo: http://demodrupal.com/
Drupal is fairly easy to use but if you need more drupal will provide you with many flexibility. Sometimes drupal is categorized as cms and also web framework. It has many add ons, theme systems using Smarty, PHPTal, or plain PHP, and supported by jquery framework for javascript and ajax capabilities.
Some of famous websites powered with drupal are Warner Bros. Records , Yahoo , Forbes , The Onion , and AOL .
2. WordPress
download:http://wordpress.org/download/
demo:http://demo.talkpress.de/trunk/
WordPress is an open source blog publishing application. WordPress is the official successor of b2\cafelog. It is easy to install and huge number free plugins and themes are available in internet. You can't go wrong with wordpress for blogging but you can also use many plugins to customize it.
3. Joomla
download:http://www.joomla.org/download.html
demo:http://demo.joomla.org/
Joomla is successor of mambo cms. Easy to use and has many plugins and themes that you can get for free on its website http://joomla.org. The system includes many popular features such as blogs, polls, news flashes, web searching, language internationalization, pdf or printable version of pages, RSS feeds, and page caching. It has many communities.
4.XOOPS
download:http://www.xoops.org/modules/core/
demo:http://demo.opensourcecms.com/xoops/
XOOPS is a free content management system written in PHP. It's allowing you to customize, theme and update your website easily. A small installation can be used as a personal blogging or journal, but you can customize to store content in news, forums, downloads and more.
5.eZ Publish
download:http://ez.no/download/ez_publish
demo:http://ez.no/ezpublish/demo
ez Publish is freely available content management system. You can use it to create websites from personal homepages to multilingual corporate website. It supports multi user access, e-commerce, and online communities.
6.CMS Made Simple
download:http://www.cmsmadesimple.org/downloads
demo:http://opensourcecms.com/index.php?option=content&task=view&id=452
Not too much talking about it, it is easy to install, configure and use :).
7.e107
download:http://e107.org/edownload.php
demo:http://demo.opensourcecms.com/e107/
It has simple easy to use theme system, integrated forums system and easy admin system. Has support for multi user and very suitable for community portal website.
8.Elgg
download:http://elgg.org/downloads.php
demo:http://test.elgg.org/
Elgg is open source cms specialized in social network websites. It is new but already win Infoworld Best of Open Source Software in 2008 for social network platform. It supports Profile, Dashboard, Blogging, Forums, Social Bookmarking and File Repository. Some social networking site powered with elgg are UnLtdWorld http://www.unltdworld.com/, Snippr http://www.snippr.de/, Rucku http://www.rucku.com/ and University of Brighton http://community.brighton.ac.uk/.
9.TYPOlight
download:http://www.typolight.org/download.html
demo:http://www.typolight.org/demo.html
As one of the best CMS it came from TYPO3, what different is that it is more easy to use and supports web 2.0. Has multi user capability, unique undo utilities, content type range from articles, news, flash content, form generator, calendar/events, newsletters to FAQ.
10.dotCMS
download:http://www.dotcms.org/download/
demo:http://www.dotcms.org/demo/
This cool cms is easy to use and easy to learn. It is reliable for personal website as to company website. Has feature such as blog, articles, news, articles, photo gallery and easy template.