Zoom is a Z-Machine, which means that it plays text adventure games written in ZCode. The original games were written by a company called 'Infocom' in the 80's: these are available on the Infocom Masterpieces CD, published by Activision.
The Mac OS X version supports all the features of the X-Windows version, has a much better user interface, and supports several extra features, such as speech output.