LiveJournal.org is the "non-profit" wing of LiveJournal.com.
While
LiveJournal.com, the site, relies on money from users to pay for the servers
and bandwidth, the LiveJournal code remains free.
The LiveJournal source is available through CVS. More information on the CVS repository, including how to browse the source online and download it, are available at cvs.livejournal.org.
Changes to CVS are posted as they happen on the LiveJournal changelog.
The developers hang around lj_dev, the LiveJournal development community. Client authors should look at lj_clients.
Much of the documented developer information, including the database scheme and the client protocol, is available at LiveJournal.com's developer area.