blkarray -- extensions and modifications of tabular support

This package is even less supported than any of David Carlisle's other
packages. It was written a long time ago, and is still documented using
the conventions of LaTeX2.09 (although it appears to work with current
LaTeX releases).

In 2014 it had a minor update to work with LaTeX2e font initialisation
and in 2015 a second update to avoid a clash with amsmath's use of box0.

Apart from these couple of lines all the code dates back to 1992 and
was more of a thought experiment than production code.
However people seem to find uses for it.

It is not really a package for using in documents in
its present state, but if you are interested in coding tables of
various sorts in TeX, you may be interested to experiment with it...
