The Free On-line Dictionary of Computing (19 January 2023):

OpenTransport
OT

    (OT) A complete reimplementation of all levels of
   the Macintosh networking code including "Classic"
   AppleTalk and MacTCP.  It appeared in MacOS revision
   7.5.3 [or earlier?  Date?].

   (2000-08-13)


The Jargon File (version 4.4.7, 29 Dec 2003):

OT
 //

    [Usenet: common] Abbreviation for “off-topic”. This is used to respond to a
    question that is inappropriate for the newsgroup that the questioner posted
    to. Often used in an HTML-style modifier or with adverbs. See also TAN.