Atarisoft published 12 official cartridges for the C64 between 1983 and 1984. Those can be seen on the Atarisoft cartridge page elsewhere on the website. However like many companies, other games were most likely in development but maybe not properly released due to the software crash. Crystal Castles is quite likely one of these titles. As it turns out, the game was eventually released, being brought over to Europe by US Gold on "limited release" in the Xmas of 1986. Unlike other prototypes, this one therefore has some curiosity value in that the official release was not published on the same medium. In the end, this version is not as good as the program Thundervision released. Grab the dump crt file and give it a whirl.