This article will be structured in two parts. The first discusses reasons to use or not use LaTeX to typeset your document, while the second discusses the current landscape of TeX engines, document typesetting systems, and distributions.
1. Introduction: do you really need to use TeX?
Back in its early days, the TeX typesetting system may have been the premier typesetting solution. This is no longer true for many use cases. Popular, commercial typesetting systems have matured considerably over the last decade. Word 2007 incorporated native equation composition which markup is actually more semantically expressive than TeX’s, and Word 2010 incorporated support for ligatures. Barring mathematical typesetting, I believe (but cannot testify) that solutions offered by Adobe (especially InDesign) and Apple come close to, or surpass, the TeX system. In addition, the WYSIWYG nature of most of these solutions’ UX lend them a tighter REPL.
What redeeming qualities, then, does typesetting in the TeX system offer? To me, there are three app-killers; one is the ability to make document-global edits through two mechanisms: TeX macros, and good ol’ search-and-replace. These features, lacking in affordable WYSIWYG editors, allow us to replace a fallible hunt-and-peck editing operation with a quick, straightforward one. The other is the number of packages that facilitate typesetting many non-conventional texts. The last, of course, is that it is free.
It is not infrequent, during the composition of a document, that you find it necessary to change the appearance or treatment of a certain class of text, say the placement of floats or bullets of a list. As far as I know, outside of theming, Word does not offer a reliable mechanism to perform such document-wide changes reliably, and I am uncertain, but skeptical, about other commercial WYSIWYG solutions.
A TeX system, on the other hand, allows us to define macros that specify markup, and define them in the document preamble, hence localizing markup. TeX macros offer another advantage: they allow us to specify semantic markup for (document-local) classes of text rather than having to resign ourselves to presentation markup. By semantic markup for document-local classes of text, I mean notions that are not universal in all documents that need to be typeset and hence are not offered in WYSIWTG systems. Examples include conjugation tables template for language books, theorem environments, the first occurrence of new jargon in a textbook, todo placeholders to indicate further writing/editing needed, etc. Tne advantage of semantic markup is that we can easily change the presentation of these classes fromj one location, and that we can easily extract such classes of text for other purposes (e.g. creating flashcards from jargon introduced in a textbook)
The other mechanism is its amenability to search-and-replace operations. Where we want to make changes on some but not necessarily all markup that fit a pattern, we can easily create a regex for it (though not foolproof, since regex, being regular, has trouble with context-free notions). This is not possible in WYSIWYG documents, since much presentation markup is hidden behind menus and not directly editable as text, and since there is the occasional piece of text that appears the same but has a different markup.
Macros and visible markup taken together mean that it is far easier to ensure consistency in a LaTeX-typeset document than one from a WYSIWYG editor.
Packages and versatility
TeX was born in academia, and the packages in a typical TeX distribution reflects that. There are packages that provides theorem environments for mathematicians. There are packages for typesetting editions of ancient manuscripts. There are packages that enable more creatively typeset passages required by some genres of poetry. There are packages that allow one to typeset a deluge of footnotes as a paragraph, which is often found in critical editions of literature. There are packages for typesetting code listings and for pseudocode. Hence if your document requires unusual typesetting that nevertheless is already popular and conventional among a group of specialists, chances are you’ll find a package for that.
After weighing the pros and cons, if you are still interested in typesetting a document in LaTeX, and are interested in producing a document beyond the generic Computer Modern look, read on.
2. Engines, Document Preparation Systems, Distributions
Beyond TeX and pdfTeX, the XeTeX and LuaTeX engines.
The TeX program by Knunth, while stable and complete, nevertheless was born too early and misses out on three important developments in digital typesetting: the PDF format, and OpenType. The output of TeX is a DVI file, which while convertible to a PostScript or PDF file, lacks PDF features like PDF hyperlinking, PDF forms, and PDF table of contents, etc.
To remedy this (and introduce a couple other features), pdfTeX was born, that primarily compiled directly to PDF files.
Nevertheless, neither TeX nor pdfTeX support newer font technologies such as TrueType and OpenType. Among others, TrueType and OpenType formats allow font distributors a standardized way to specify and provide support for many typographic features; specifying different features for different languages and scripts, support for small caps, superscripts, subscripts, lining figures, old-style figures, proportional figures, ligatures, optional ligatures, combining accents, contextual alternatives, etc., all in a single, customer-friendly font file. Hence typographers have embraced OpenType. My favorite examples of the versatility of OpenType comes from Kazuraki and Zapfino Arabic.
The XeTeX engine introduced compatibility with OpenType fonts.
Current development, however, is focused on LuaTeX. As the name suggests, LuaTeX is an engine that exposes Lua bindings. It is also designed to be compatible with XeTeX documents, supporting OpenType as well, though having different internals.
The TeX program, along with its macro language, was invented before the benefits of proper encapsulation in structured programming and in object-oriented programming were widespread and accepted. In addition, TeX lacks first-class support for numerical computation. All these legacy decisions mean that writing involved macros and macro packages often involve a fair number of kludges and side cases, arcane, non-obvious code, and non-obvious incompatibilities with other packages. LuaTeX is a step towards alleviating this situation, along with LaTeX3 (though the latter’s pace of development makes Perl 6 look like the Road Runner.)
In between, there have been other TeX-like engines being developed such as NTS, ExTeX, Omega and Aleph, though their functionality have been largely superseded by newer engines.
TeX, LaTeX and ConTeXt
Documents compiled by any one of the above engines can be said to be TeX, LaTeX, or ConTeXt documents. TeX documents have to specify themselves the presentation of their elements somewhere. LaTeX is a macro framework sitting on top of TeX that specifies sane defaults, guided by an objective of allowing the author to care as little about the presentation of their document if desired; LaTeX documents assume that they will be compiled along with the LaTeX. As a result, it is not always straightforward to change certain aspects of a LaTeX document. ConTeXt is another macro framework incompatible with LaTeX, but ConTeXt is far more customization-friendly out of the box. The latest version of ConTeXt supports only LuaTeX, utilizing its modern feature set. Both LaTeX and ConTeXt specify mechanisms to import third-party packages. Ultimately, however, for better or worse, LaTeX, perhaps by virtue of being more accessible than TeX and of having been started earlier than ConTeXt, is the target of most third-pary packages being distributed freely.
Whereas there used to be a variety of TeX distributions, TeX Live for Linux and Windows and its twin MacTeX have emerged to be the superior, albeit slightly weighty, standard distribution. They are maintained by the TeX Users Group and come with utilities to regularly update or auto-update from the CTAN (Comprehensive Tex Archive Network) mirrors. Being somewhat of a niche piece of software, CTAN packages do not often update as frequently as those in repositories for OSes, popular programming languages, etc.
I hope this clarifies for the reader what the words and differences between TeX, LaTeX, ConTeXt, pdfTeX, XeTeX, LuaTeX, CTAN, etc. are, and gives an insight into the development history of the TeX ecosystem. If TeX is right for you, I encourage you to try out the newer engines and try out some novel customizations. To that end, I am writing a companion post which is an annotation of a template that I base my documents off.