WordPress MU, or WordPressµ, is the multi-user version of the famous WordPress blogging application. It is ideal for people who want to set up a large network of blogs. Please see forums at MU.WordPress for discussion.
WordPress MU is the underlying software that powers the WordPress.com hosted blogging service. WordPress MU is also used by newspapers, magazines, blog networks, universities and large companies running corporate blogging systems behind firewalls.
Using the WordPress multi-user edition, you will be able offer your users an opportunity to sign up for a new blog. They will be able to securely manage their templates and settings without affecting any other users. You can have unlimited users with unlimited blogs, and users can have various roles (admin, editor, author, contributor, subscriber) on each other's blogs. One or more Site Administrators can perform site-wide management tasks, including adding users and blogs, altering permissions and granting access to themes.
WordPress MU is a unique WordPress product. Plugins and themes are controlled by a central system administrator. So unlike the single-user version of WordPress, individual MU bloggers cannot upload their own plugins and themes, only select from the ones made available by the system administrator. Individual themes can be made available to all blogs or just to specific ones.
While WordPressMU users are blogging with a limited version of WordPress, and currently are able to choose from a list of included WordPress Themes and have little customization, there are still a lot of benefits.
WordPress MU is designed for hosts to offer hosting of WordPress blogs to individual users. The full version of WordPress is still free and available for download, and it is designed to offer full customization for the single or multi-user blogs and/or multiple blogs by a single administrator.
Installing WPMU has some documentation on installing.
For support and information on installing and using WordPress MU, visit the WordPress MU website and support forum. A WordPress MU system is more complex to maintain than a single-user WordPress system, so timid or casual user beware.
If you are a WordPress MU user click on the Feedback button in your Dashboard. Some help may be found within the WordPress Codex in the articles listed in the next section or in Donncha's FAQ.
There is the WPMU IRC Channel for real time help and chat.
This link returns recent changes to WPMU Related Codex pages.
The following is a list of documentation on the WordPress Codex that may help answer your questions about posting, creating categories and Pages, and managing your WordPress blog on WordPressMU.
For answers to specific questions on WordPress MU, check out the WordPress MU Support Forum.
To report bugs, see the Debugging WPMU guidelines
A WikiMedia based documentation site has been established for WordPress MU at http://www.wpmuwiki.org and is open for contributions.
WPMU Adoption Articles pulls together some threads useful for gaining traction on your WPMU site.
WPMU FAQs lists various FAQ sources.