The entire model was totally different. Door games were usually shareware. Authors wanted sysops to pay a registration fee, and they used different tactics to e

The entire model was totally different. Door games were usually shareware. Authors wanted sysops to pay a registration fee, and they used different tactics to encourage that. Sometimes the game had extra features crippled unless you registered; sometimes there was a time limit after which the game would be unplayable if you didn't register. But note that the registrations were paid by SYSOPS rather than the individual end users. (Though sometimes users on a BBS would chip in together to help their sysop register a favorite game)