HP-18C business consultant, 1986
An advanced business model, the HP-18C calculator had a "clamshell" design, opening like a book with two keyboards facing each other inside. It included graphing and a date-time-alarm feature similar to a personal organizer. The 18C had 2K of memory and was priced at $175.
The HP-18C was the first in a series of "clamshell" calculators produced by HP.