SILE is described as ', abbreviated for Simon's Improved Layout Engine, is a typesetting system, whose job is to produce beautiful printed documents from raw content'. There are five alternatives to SILE for Mac, Linux, Windows and BSD. The best alternative is LaTeX, which is both free and Open Source. Other great apps like SILE are Pollen (Free, Open Source), MacTeX (Free, Open Source), ConTeXt (Typesetting System) (Free, Open Source) and Groff (Free, Open Source).
LaTeX is a document markup language and document preparation system for the TeX typesetting program. The term LaTeX refers only to the language in which documents are written, not to the editor used to write those documents. In order to create a document in LaTeX, a .
MacTeX is a redistribution of TeX Live, a typesetting environment. While TeX Live is designed to be cross-platform (running on Unix, Mac OS X, and Windows), MacTeX includes Mac-specific utilities and front-ends.
“a system for typesetting documents based on TEX and METAPOST. You can use this system for converting documents coded in TEX format as well as documents coded in XML into high quality PDF” (http://www.pragma-ade.