Alfresco is available for Windows, Mac, and Linux operating systems, and is available in two different formats: Community (open source, free version) and Enterprise--the paid version recommended for businesses and large corporations.
Alfresco has several other products, all available with no upfront costs, to assist with document management, records management, image management, and project collaboration. If support is desired, users have the option to purchase a yearly subscription to have access to all the same things in the Enterprise Edition.
Installation instructions and tutorials can be found at the Alfresco Studio Wiki. Other information about the suite can be found at the Alfresco website.