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. Trying to make a pretty sign in a markup language would probably hurt...
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.
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.
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.
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 GNOME project also is working toward various GNU-licensed officey tools. None are available yet, though.
At least Caldera and Red Hat ship packages containing the usual office apps like a WYSIWYGish word processor and a spreadsheet. I would assume they do a dandy job, but I've never used them. I think Caldera also ships Sun's WABI, so you could probably run something like MS Office under that if you had to integrate with other folks' files.
Jeff Phillips <jeff@I_RATUS.org> uses Caldera's WordPerfect
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.
RedHat and SuSE ship a suite called Applixware; you can find their web site at http://www.redhat.com/. Applix is available on many platforms, and includes a spreadsheet, word processor, a presentation package, and so on. There is a separate version of Applix available in Java called ApplixAnyWhere; I would assume it's much the same, but slower and less featureful.
Other vendors should feel free to drop me a line with your offerings.