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

nagware
 /nag'weir/, n.

    [Usenet] The variety of shareware that displays a large screen at the
    beginning or end reminding you to register, typically requiring some sort
    of keystroke to continue so that you can't use the software in batch mode.
    Compare annoyware, crippleware.


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

nagware

    /nag'weir/ A term, originally from Usenet, for the
   variety of shareware that displays a message on start-up and/or
   termination reminding you to register, pay or donate (see
   guiltware).

   Sometimes user interaction is required to dismiss the nag in order
   to use the program, making it useless in batch mode.

   Nagware may also be crippleware, with a message nagging you pay
   to upgrade to the full or "pro" version.

   [Jargon File]

   (2015-01-17)