opensourceCMS: This site has several dozen installed CMSs for you to play with:
“This site was created with one goal in mind. To give you the opportunity to ‘try out’ some of the best php/mysql based free and open source software systems in the world. You are welcome to be the administrator of any site here, allowing you to decide which system best suits your needs.”
It will only install PHP/MySQL-based systems that are open-source (free) and can run on hosted servers.