I've added details to the README to hopefully explain why it exists: https://github.com/johnsonjh/OpenVi#why
The OpenVi ChangeLog at https://raw.githubusercontent.com/johnsonjh/OpenVi/master/Ch... includes all the history going back to 1993's Nvi 0.93. Nvi 1.79 was released in 1996, which is the version OpenBSD's vi was derived from.
The ChangeLog entries are only a summary of the full commit messages - the complete details are in OpenBSD's CVS tree, and viewable a bit easier via GitHub (https://github.com/openbsd/src/commits/master/usr.bin/vi)
Changes to the (OpenVi bundled) OpenBSD regular expression engine are not included in the legacy ChangeLog, but you can see that development in the CVS tree or via GitHub as well (https://github.com/openbsd/src/commits/master/lib/libc/regex).
OpenVi also utilizes the OpenBSD version of Berkely DB (https://github.com/openbsd/src/commits/master/lib/libc/db).