Vi is the original screen based text editor for Unix systems.
It is considered the standard text editor, and is available on
almost all Unix systems.
Nvi is intended as a "bug-for-bug compatible" clone of the original
BSD vi editor. As such, it doesn't have a lot of snazzy features as do
some of the other vi clones such as elvis and vim. However, if all
you want is vi, this is the one to get.