Hugo is one of the leading IF design systems. In addition to being capable of producing leading-edge text adventures, it also allows a developer to incorporate true-color graphics display (which are optional for those who lack either the hardware or inclination to view graphics) as well as sound effects and music. And it's free.

The complete Hugo system consists of several parts, the most important of which are the Hug Compiler and the Hugo Engine--the former takes text-format source code and turns it into a playable format understood by the latter. The Hugo language itself is an easy to learn, highly object-oriented language which (the author hopes) encompasses the best elements of elegance, simplicity, clarity, and power of modern programming languages. Also available is the Hugo Library: a collection of common routines, objects, etc. that are responsible for managing many of the "physical universe" aspects of the game. (And the sophisticated Hugo Debugger allows a Hugo programmer to examine every aspect of a game at runtime.)

License: free