We list here the free or shareware packages; another question addresses commercial TeX vendors' products.
ftp are to be found in
unixtex.ftp, though nowadays the sensible installer will
take (and possibly customise) one of the packaged distributions such
as teTeX, or the TeX Live distribution.
To compile and produce a complete teTeX distribution, you need a
.tar.gz file for each of teTeX-src,
teTeX-texmf and teTeX-texmfsrc.
No sets of teTeX binaries are provided on CTAN; however, compilation of teTeX is pretty stable, on a wide variety of platforms. If you don't have the means to compile teTeX yourself, you will find that most "support" sites carry compiled versions in their "free area", and the TeX-live discs also carry a wide range of binary distributions.
During periods when teTeX is itself under development, a "teTeX-beta" is available. Before proceeding with the beta-release, check the ANNOUNCE files in the two directories on CTAN: it may well be that the beta-release doesn't offer you anything new, that you need.
MacOS X users should refer to the information below, under item "Mac".
The most recent offering is a free version of the commercial VTeX, which among other things, specialises in direct production of PDF from (La)TeX input.
A version of emTeX, packaged to use a TDS directory structure, is separately available as an emTeX 'contribution'. Note that neither emTeX itself, nor emTeXTDS, is maintained. Most users of Microsoft operating systems, who want an up-to-date (La)TeX system, need to migrate to Win32-based systems.
texmf tree as a teTeX installation). fpTeX's
previewer (Windvi) is based on xdvi, and takes
advantage of extra facilities in the Win32 environment.
Windvi is capable of printing directly, and a version of
dvips is also available.
MikTeX, by Christian Schenk, is also a comprehensive distribution, developed separately from the teTeX work. It has its own previewer, YAP, which is itself capable of printing, though the distribution also includes a port of dvips. The current version is available for file-by-file download (the HTML files in the directory offer hints on what you need to get going). The MikTeX developers provide a ready-to-run copy of the distribution (for purchase) via the MikTeX web site.
ProTeXt, by Thomas Feuerstack, is a further option for installing MikTeX. It bundles a MikTeX setup with some further useful utilities, together with a PDF file which contains clickable links for the various installation steps, along with explanations. It again it is freeware, and copies are distributed with the TeX-live CD set.
A further (free) option arises from the "CygWin" bundle, which presents a Unix-like environment over the Win32 interface; an X-windows server is available. If you run CygWin on your Windows machine, you have the option of using teTeX, too (you will need the X-server, to run xdvi). Of course, teTeX components will look like Unix applications (but that's presumably what you wanted), but it's also reputedly somewhat slower than native Win32 implementations such as MikTeX or fpTeX. TeTeX is available as part of the CygWin distribution (in the same way that a version is available with most Linux distributions, nowadays), and you may also build your own copy from the current sources.
BaKoMa TeX, by Basil Malyshev, is a comprehensive (shareware) distribution, which focuses on support of Acrobat. The distribution comes with a bunch of Type 1 fonts packaged to work with BaKoMa TeX, which further the focus.
UK TUG prepays the shareware fee, so that its members may acquire the software without further payment. Questions about OzTeX may be directed to oztex@midway.uchicago.edu
Another partly shareware program is CMacTeX, put together by Tom Kiffe. This is much closer to the Unix TeX setup (it uses dvips, for instance). CMacTeX includes a port of the latest version of Omega.
Both OzTeX and CMacTeX run on either MacOS X or on a sufficiently recent MacOS with CarbonLib (v1.3 for OzTeX, v1.4 for CMacTeX). MacOS X users also have the option of gwTeX, by Gerben Wierda (which is based on teTeX). This is naturally usable from the command line, just like any other Unix-based system, but it can also be used Mac-style as the engine behind Richard Koch's (free) TeXShop, which is an integrated TeX editor and previewer.
A useful resource for Mac users has a news and 'help' section, as well as details of systems and tools.
If anonymous ftp is not available to you, send a message
containing the line 'help' to
atari@atari.archive.umich.edu
ftp from ftp.math.utah.edu
in pub/tex/pub/web
This question on the Web: http://www.tex.ac.uk/cgi-bin/texfaq2html?label=TeXsystems