Calixto Island was one of the 2 Mark Data Products text adventure games, and is a port of an earlier version that that they did done for the hobbyist 6800/6809 market (it was originally released for the 6800 version of Flex as of the April 1981 issue of 68 Micro Journal magazine). In the July 1981 issue of the same magazine they announced that the Coco version was coming soon, and by the August 1981 issue it was officially on sale (alongside it's younger sibling, The Black Sanctum). The game featured save/load games in progress (originally to tape, later to disk). The premise of the game is that one has to explore Calixto Island and find a treasure - and then return it to it's rightful place. It uses a then standard verb/noun parser.
Title: Calixto Island
Authors: Ron Krebs
Publisher: Mark Data Products
Released: August 8, 1981
Requires: Color Computer 1,2,3, 16K RAM, tape or disk.
Download CALIXTOT.ZIP (contains DSK image). LOADM"CALIXTO":EXEC to run. NOTE: This does not seem to work properly on a Coco 3, just a Coco 1 or 2. For the Coco 3, try the graphic version.