MacTCP is the standard TCP/IP implementation for the classic Mac OS through version 7.5.1.
It is the first application-independent implementation of a TCP stack for a non-Unix platform[1][2] and predates Winsock by over 5 years.
Released in 1988, it is obsolete and has reliability issues and incomplete features that sometimes prevent it from operating properly on the modern Internet.
It was originally a substantial purchase, at $2,500 (equivalent to $6,000 in 2023) for a site license, with an additional $2,500 fee for commercial use.
MacTCP is included free with System 7.5,[3] when the rising popularity of the Internet made it a necessity.