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

MacTCP

    Part of earlier versions of MacOS that provided
   access to TCP/IP services.  Apple removed MacTCP from
   MacOS in revision 7.5.3 in favor of the new OpenTransport
   (OT) TCP/IP stack.  However, MacTCP lives on as a community
   development effort.

   See also MacPPP.

   [How did it work?  Where was it from?]

   (2000-06-25)