Intermail is a front-end mailer, written by some of the the coders who wrote Frontdoor, and thus very similar in appearance and functions. Very popular, surely in part because of the extreme simplicity in procuring a serial number. The built-in screensaver, which consists of the word Intermail popping up at a random spot on the screen in a random ansi fg/bg colour combination, is incredibly hypnotic. I've spent so many hours staring at it, waiting for users or mailers to call my board.