What was the first package for typesetting commutative diagrams in Latex and when was it made available?
You can find a comparison between packages for commutative diagrams in a very nice paper by Gabriel Vicente Feruglio on TUGboat, issued in 1994.
According to the bibliography, the first available package (besides using directly
picture mode) was the one by John Reynolds,
diagmac.sty issued in 1987 and still available as
diagmac2 (some patches were introduced by Bob Tennent in order to make the package use
The porting of AMS-TeX to LaTeX pushed several people to do the switch and this prompted the development of the other packages described in Feruglio's paper.