You can download Feng Office Community Edition for free, and use it at no charge, forever.
In order to install Feng Office on your own Server you need to correctly setup a Web Server (Apache 2.2 recommended) with PHP 5 and a MySQL database with InnoDB support.
Free downloads of the Community Edition do not grant access to Feng Office Support Plans. If you plan on using Feng Office on a Business Environment, we recommend you check out the Support Plans and Pricing for the Professional Edtion.
If you just want to try out Feng Office you can sign up for a free trial here.