Download AMS-TeX version 2.2 (amstex.zip) br> This archive will unpack into an existing TEXMF structure, in most cases providing a ready-to-use installation.
AMS-TeX is a TeX macro package designed for writers whose material contains a substantial amount of mathematics. AMS-TeX provides high-level commands for many of the more complicated constructions that commonly occur in mathematical formulas---constructions that typically cannot be written in plain TeX except by laborious aggregation of lower-level commands, along with trial-and-error adjustments to the spacing and positioning of the constituent elements.
AMS-TeX was one of the first major macro packages written for TeX; a preliminary version (for TeX78) was publicly available as early as 1981; version 1 of AMS-TeX was available effectively by late 1984. Michael Spivak, the author of AMS-TeX, also wrote a reference manual, The Joy of TeX , which is published by AMS.
AMS-TeX is essentially a superset of of the plain TeX macro package that focuses on adding features for dealing with advanced mathematics. In adapted form, those features are accessible in LaTeX through an amsmath package provided in the AMS-LaTeX collection.