LaTeX

LaTeX is a markup language for generating print-quality typesetting.
It is mostly used academic circles, primarily in the natural sciences, for creating material for scientific publications.

How it works

A LaTeX document structure is comparable to HTML: There is a preamble which indicates some basic, overall features of the document, and there is the main document with the relevant markup for formatting.

Code example

\documentclass[12pt,a4paper,notitlepage]{article}
\usepackage[utf8x]{inputenc}
\usepackage{ucs}
\usepackage{amsmath}
\usepackage{amsfonts}
\author{Morten Juhl Johansen}
\title{LaTeX article}
\begin{document}
This is the beginning of an article on \LaTeX!\\
There are \textbf{bold text}, \textit{italics}, \underline{underscoring}, footnotes\footnote{this is a footnote}\\
- and lots of other goodies. A math example:
\begin{equation*}
\sum_{n=1}^\infty
  \frac{1}{n^2}= \frac{\pi^2}{6}.
\end{equation*}
\end{document}