Evangelion Kaibunsho is an document about Hideaki Anno and Evangelion posted to the Internet anonymously in February 1997 by a self-professed "anime industry dropout" who claimed to have worked on the Eva project. It makes a number of tantalizing claims about Anno, including the identity of Anno's first true love, his early relationship with Hayao Miyazaki, and some original endings Anno had in mind for Eva. It is (and probably will remain) unknown how true or reliable the claims made in the Kaibunsho are.
What's a Kaibunsho?
In Japanese society, Kaibunsho are "mysterious documents" of unknown origin that expose sensitive information about particular targets. Many scandals in Japan involving business, entertainment and political figures are triggered by kaibunsho such as leaked memos, reports, etc.
English translation and reception
In late 2006, relevant parts of the Kaibunsho were translated into English by Bochan Bird and posted to Evaotaku.com. One of the most extended responses was a series of posts by Carl Gustav Horn here, here and here. Carl is the editor of the English release of the Evangelion manga, and has extensive knowledge in Gainax and Eva-related affairs. He considers the document to be largely unreliable and inaccurate, save for some information which was previously available elsewhere.