WordPress
This is the most CMS that was using by many people.
WordPress started in 2003 with a single bit of code to enhance the typography of everyday writing and with fewer users than you can count on your fingers and toes. Since then it has grown to be the largest self-hosted blogging tool in the world, used on hundreds of thousands of sites and seen by tens of millions of people every day.
Homepage:http://wordpress.org/
Download:
Download WordPress 2.5.1 (zip)
Download WordPress 2.5.1 (tar)

Jojo
Jojo is a PHP based free CMS for web developers wanting to build good websites. We like sites that are fast, standards compliant, easy to manage, search engine friendly and easy on the eye.

Homepage: http://www.jojocms.org/
Download: Jojo CMS 1.0 Release Candidate 1
ZIP archive (6.55M)
7z archive (3.8Mb)

Saurus CMS
Saurus CMS Free package targets sites with up to 150 content items and comes as the name says, free of charge. Even better, the updates are free as well. The free edition limits the amount of content items. Otherwise the functionality is exactly the same as in Saurus CMS SE package.

Homepage: http://www.saurus.info
Download: Saurus CMSVersion 4.5.0
SaurusCMS-4.5.0.tgz (5.8 MB) - TGZ for installing on Linux.
SaurusCMS-4.5.0.zip (6.7 MB) - ZIP for installing on Windows or on Linux when you have only FTP access to the server.
SaurusCMS-4.4.0.exe (42.6 MB) - EXE file for quick setup in Windows 98/Me/NT/2000/XP. It installs Saurus CMS, PHP, Zend Optimizer, MySQL and Apache. If you already have these applications, use the ZIP package instead. Use username "admin" and password "saurus" to log in first time when installing this installer.

TYPO3
TYPO3 is a free Open Source content management system for enterprise purposes on the web and in intranets. It offers full flexibility and extendability while featuring an accomplished set of ready-made interfaces, functions and modules.

Homepage: http://typo3.com/
Download: Version 4.2.1
Dummy tar.gz
Dummy ZIP
*If you don't have a webserver and want to test TYPO3 on your local PC, download one of the Installers.

Frog CMS
Frog CMS simplifies content management by offering an elegant user interface, flexible templating per page, simple user management and permissions, as well as the tools necessary for file management.

Frog requires PHP5, a MySQL database or SQLite 3 with PDO, and a web server (Apache with mod_rewrite is highly recommended). It is distributed under the MIT software license.

Frog is unique because of its simple templating code. Because it uses PHP directly, there is no need to learn yet another scripting language.

Homepage: http://www.madebyfrog.com/
Download: version 0.9.2 zip, version 0.9.2 tar.gz

Movable Type
Movable Type offers a powerful summary of your blogging activity via a convenient single screen. Dynamic graphic displays let you see what's happening with your blogs, which content and which contributors are driving conversations, and provides smart starting points for managing your site.

Homepage: http://www.movabletype.org/
Download: Movable Type 4.12