Close-up was a customer support communications program developed by Norton-Lambert Corp. and written by Cogitate, Inc. It allowed one personal computer running DOS

DOS

DOS, short for "Disk Operating System", is an acronym for several closely related operating systems that dominated the IBM PC compatible market between 1981 and 1995, or until about 2000 if one includes the partially DOS-based Microsoft Windows versions 95, 98, and Millennium Edition.Related...

 to see the screen contents of another PC and send keystrokes as well. Both PCs communicated via the use of a modem

Modem

A modem is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data...

. Version 4.01 was available in 1992.