#cloakofdarkness

Dedalus - A system based on Javascript and HTML to generate and run Choose Your Own Adventure narrative

Yes, another web-based choice-type system. This one looks pretty neat and worth checking out. On github: https://github.com/pistacchio/Dedalus

Inform is one of the most popular language for interactive fiction, at least assuming interactive fiction equals parser-based interactive fiction, where the player types in commands. There are also other authoring languages. 

Inform actually comes in two different versions, Inform6 and Inform7.

To get a feel for the difference, have a look at these two examples:

Object foyer "Foyer of the Opera House" with description "You are standing in a spacious hall, splendidly decorated in red and gold, with glittering chandeliers overhead. The entrance from the street is to the north, and there are oorways south and west.", s_to bar, w_to cloakroom, n_to "You've only just arrived, and besides, the weather outside seems to be getting worse.", has light;

Inform 7:

Foyer of the Opera House is a room. "You are standing in a spacious hall, splendidly decorated in red and gold, with glittering chandeliers overhead. The entrance from the street is to the north, and there are doorways south and west." Instead of going north in the Foyer, say "You've only just arrived, and besides, the weather outside seems to be getting worse." The Cloakroom is west of the Foyer. The Bar is south of the Foyer.

(These are, by the way, both parts of the source code of Cloak of Darkness, which has become a standard example of doing something in different IF languages. The full Inform6 source code is here and the Inform7 version is here). Other versions are available at the Cloak of Darkness page.

Both of these languages are in use, and you can develop in both of them in the Inform IDE, which you can download from Inform7.com.