MiKTeX (pronounced mick-tech) is an up-to-date implementation of TeX/LaTeX and related programs for Windows (all current variants). TeX is a typesetting system written by Donald Ervin Knuth who says that it is "intended for the creation of beautiful books - and especially for books that contain a lot of mathematics".
A complete set of additions (programs, styles, fonts, …) are available to help you typeset your documents. The TeX output viewer Yap allows for an optimized edit-compile-view cycle (if the TeX authoring system in use supports source specials).
This distribution includes TeX, pdfTeX, XeTeX and LuaTeX.