[xel02]

LaTeX is a typesetting program (related to TeX which was made by Knuth). Its quite popular in academia (sciences at least) because it handles equations really well.

Its analogous to a markup language in that it is not a WYSIWYG typesetting program.

[eru]

LaTeX is also useful [1] for controlling Mars rovers. See page 5 of the current Monad Reader (http://www.haskell.org/sitewiki/images/8/85/TMR-Issue13.pdf).

[1] OK, not actual useful, but it can be done.