GNU software distributions, freely available, for example, at
<ftp://sunsite.cnlab-switch.ch/software/mirror/gnu/>, usually incorporate
lots of English-language documentation in several of the categories you
mention. You'll have to download and unpack the whole distribution of a
particular package and then poke around its source code tree to find its
documentation; the file =README-about-.gz-files gives terse instructions on
the unpacking stage. See <http://www.fsf.org/doc/doc.html> for more
information.
If you step up a level, to
<ftp://sunsite.cnlab-switch.ch/software/mirror/>, you're looking at lots
more stuff. For example, the cert directory leads to bulletins from the
computer emergency response team. And so on.
-- Dominic Dunlop