EDMAC is a program written as a set of plain TeX macros for formatting complex critical editions. You mark up your text and notes using the tags provided by EDMAC, and then TeX will create a beautiful book for you with the text line numbered, lemmata referred to by line-number, up to six layers of notes at the bottom of the page (variants, testimonia, etc.), as well as up to six sets of notes sent to appendices. It is also possible to control the layout of each layer of notes separately: single column, two- or three-column, paragraphed, etc.
or typesetting critical editions in the traditional manner with LaTeX, we [i.e.: see bottom] know of two macro packages:
* ednotes.sty by Christian Tapp and Uwe Lück;
* ledmac by Peter R. Wilson.
When both packages were devised, critical edition typesetting with TeX required the EDMAC macros by Dominik Wujastyk and John Lavagnino. EDMAC, however, is not compatible with LaTeX, which many prefer to Plain TeX. So ledmac was written as (almost) a port of EDMAC to LaTeX (while its functionality has increased much since). ednotes was written as an attempt at a somewhat smarter user interface than that of EDMAC.