ccHost is a PHP library intended to be installed on web servers wishing to host CC licensed content, either by individuals or entire communities. ccHost music files, images, videos and zip archives. Extending the type of files hosts is done easily.
PHP or HTML programming is not required to set up a ccHost installation.
For all practical purposes, ccHost is a CMS specializing in CC licensing, 'remix' (revision) tracking and community features.
It is located here http://ccmixter.org/media/viewfile/isitlegal.xml. There is much information at the aforementioned link which can help in answering your questions.
There are so many ways to contribute to the development of ccHost. One of the best ways is by submittig bug reports and filing feature requests. Other ways to contribute are to contribute code (patches), to answer questions on the mailing list and on the chat channel. Doing any of these tasks drastically helps development.
Please see CcHost#Project_Goal.
ccMixter is one installation of the ccHost engine. ccHost can be installed for free by anyone onto a web server with Apache, mySQL and PHP and works both on Linux/Unix and windows servers.
ccMixter is the original concept for a site that would be like the "friendster for music." It has evolved much and eventually the decision was made to generalize the engine that powers ccMixter so that it could be used anywhere on multiple file formats.
No, it does not cost anything to download, install and use it.
ccHost has a generalized architecture for many popular media types of formats.