Here we get into a real rat's-nest of software. Basically, Linux can run many types of binaries with varying degrees of success: Linux/x86, Linux/Alpha, Linux/Sparc, Linux/foo, iBCS, Win16/Win32s (with dosemu and, someday, with Wine), Mac/68k (with Executor), and Java. I'll just discuss native Linux and common Unix software.
For Linux itself, choices are mostly limited to those available for Unix in general:
Most markup languages are more suitable for large or repetitive projects, where you want the computer to control the layout of the text to make things uniform.
nroffThis was one of the first Unix markup
languages. Man pages are the most common examples of things formatted
in *roff macros; many people swear by them, but nroff has, to me at
least, a more arcane syntax than needed, and probably makes a poor
choice for new works. It is worth knowing, though, that you can
typeset a man page directly into postscript with groff. Most man
commands will do this for you with man -t foo | lpr.
TeX, and the macro package LaTeX, are one of the most widely
used markup languages on Unix. Technical works are frequently written
in LaTeX because it greatly simplifies the layout issues and is
still one of the few text processing systems to support
mathematics both completely and well. TeX's output format is
dvi, and is converted to PostScript or Hewlett Packard's PCL with
dvips or dvilj. If you wish to install TeX or LaTeX,
install the whole teTeX group of packages; it contains everything.
There is at least one free sgml parser available for Unix and Linux; it forms the basis of Linuxdoc-SGML's homegrown document system. It can support other DTD's, as well.
Someone suggested that for simple projects, it may suffice to write it in HTML and print it out using Netscape. I disagree, but YMMV.
There is no longer any shortage of WYSIWYG word processing software. Several complete office suites are available, including one that's free for personal use (StarOffice).
A German company is distributing StarOffice on the net free for Linux. This full-blown office suite has all the features you'd expect, and you can't beat the price. There's a mini-HOWTO out there which describes how to obtain and install it. It generates PostScript or PCL, so should work with most any printer that works otherwise on Linux. Apparently it's an Office clone and is rather bloated.
Corel distributes a basic version of Word Perfect 8 free for Linux, and has suggested that they will distribute Corel Draw and Quattro Pro as well, once they are ported. This is probably the best option if you have an ARM machine; Corel makes the ARM-based Netwinder Linux computers and is almost certian to offer ARM Linux versions of everything. You can also buy the full-blown version and support, together or separately. The Linux WordPerfect Fonts and Printers page has information about configuring WordPerfect for use with either Ghostscript or its built-in printer drivers (which are apparently identical the DOS WordPerfect drivers, if your printer's driver isn't included in the WP8 distribution).
Applix is a cross-platform (ie, various Unices, Windows, and others) office suite sold by the Applix company. Red Hat and SuSE sold it themselves when it was the only game in town; now sales have reverted to Applix.
LyX is a front-end to LaTeX which looks very promising. See the LyX Homepage for more information. There is a KDE-styled version of LyX, called Klyx; the author of LyX and the instigator of KDE are the same person.
Maxwell is a simple MS RTF-format based word processor which started as a commercial product but is now distributed under the GPL.
AUIS includes ez, a
WYSIWYG-style editor with most basic word processor features, HTML
capabilities, and full MIME email and newsgroup support.
Unfortunately, AUIS is no longer maintained.
The KDE project is working toward a whole office suite. I don't think it's ready for prime time yet. The word processor will apparently be a descendant of LyX.
The GNOME project also is working toward various GNU-licensed officey tools. None are available yet, though.
Jeff Phillips <jeff@I_RATUS.org> uses Caldera's WordPerfect 7
for Linux (on Slackware, of all things) and says that it works well.
It apparently includes built-in printer support, as one would expect.
Caldera should have info on
http://www.caldera.com/. You
can also buy a newer version of Wordperfect directly from Corel's
chosen Unix port company.
Other vendors should feel free to drop me a line with your offerings.