The Free On-line Dictionary of Computing (30 December 2018):

ntalk
new talk

    ("new talk") An update of the Unix "talk" program,
   old versions of "talk" being referred to as "old talk".  New
   talk and old talk are generally incompatible, and attempts to
   get them to communicate result in entirely unhelpful error
   messages.

   On most modern Unix systems, the program "talk" is new talk,
   with some SunOS versions being a notable and annoying
   exception to this.

   (1997-09-11)