As far as interactive fiction creation systems go, the freeware, platform independent and constantly evolving Inform 7
is a fantastic, versatile and incredibly powerful tool, that should really appeal to writers. I can't say if it's the best one available, but I can easily assure you it's my favorite. And now, with the release of the brand new 6L02 build, it's better and more flexible than ever.
The new version, the first substantial update to the venerable authoring language in three years, introduces all sorts of improvements and widely requested features. You can read a brief outline of what's new here
Two of the most important additions are the Public Library for extensions and Inform's new ability to generate adaptive grammar. The former makes extending and adding components to your game (or educational i-f) easier than ever, whereas the latter makes writing both easier and actually doable in languages other than English. Also of note are the much needed open bug tracker, the true support for numbers and the two books that come bundled with the program's archive.
Inform 7 is available for Windows, Mac OS and Linux here