LaTeX is a typesetting language which is particularly useful for technical writing. Documents may be written using a plain text editor, with command sequences to indicate details such as headings. A particularly nice aspect is that it produces significantly better mathematical equation formatting than commercial word processors.
Note that I use the GNU/Linux operating system, so the examples on this page will work best on unix-like systems. However, the tools for other platforms are slowly catching up so the following examples can probably be adapted.