I've been working with DocBook and thinking about software documentation, and as a prelude to some entries with tips and thoughts about what I wish existed, I thought I would share what I'm currently using. The following combination works reasonably well:
DocBook XML (with the on-line book as a crutch)
Emacs (in a Mac OS X-specific package)
nxml mode (with DocBook Relax NG schemas) (For the uninitiated, here's a nice overview.)
DocBook XSL (with the on-line book as a crutch)
Saxon
RenderX XEP (I've had too many problems with FOP to use it.)
the Hibernate manual as a staring point