There are several competing versions:
https://wiki.python.org/jython/UsersGuide
(is a non-existing page which causes the wiki to list the various userguide instances as suggestions of similar pages)
There exist at least

UserGude11

JythonUserGuide

Jython User Guide

UserGuide

NewUsersGuide

My plan is to merge them into one authoritative version, and find some way to have one single source from which a user guide can be provided in the wiki (perhaps better remove it from the wiki, actually), on the homepage, and on APIdia. However, that is more like a long term plan, which I might be able to carry out later this year.

Copied the discussion from @Stewori