The Justus League was a secret board created by Xkeeper as a getaway from Acmlm's Board. The board had little activity in its short life, but it was nevertheless a haven for numerous discussions. The board was originally an invitation-only board; it was later opened to anyone who could find the web address to the board. New users were given a 15-post trial membership; to continue posting, the user must have been approved by Xkeeper.
The Justus League closed on February 17, 2007, the same day that Xkeeper resigned from his post as maintainer, owner, and coder of Acmlm's Board.
Of course, like everything else, it was eventually revived and brought back online. Instead of using a "trial member" format, there's just several levels, ranging from "public use only", to "private", to "special", with one forum for each.