The Lyceum, Lyceum is a stand-alone mutli-user blogging application, designed for the enterprise. Utilizing the fantastic, intuitive WordPress blogging engine at its core. I have been testing using it since April Last year. Even Weseepeople started over there.
But I have deployed it in two internal projects, hosting closer to 20 blogs in each site. If you are familiar with wordpress, then this is a piece of cake, just add Multiuser to wordpress.
Get it via SVN or as a .tar.gz from the downloads page.
Report bugs and feature suggestions on trac.
Get help on the support forums, email lists, or IRC channel.