Another one that's been around for decades at this point is the Inform[1] platform. There's still an active group of people who produce all sorts of interactive fiction books in the vein of CYOA books that are of surprisingly great quality.
Yet another tool of note for writing CYOA interactive fiction is Twine (http://twinery.org/), which has become a defacto standard of sorts of an interactive narrative writing tool more specifically for hypertext CYOA.
For example of its growing ubiquity, it was admitted that most of the Black Mirror Bandersnatch CYOA episode was written and tested in Twine.
[1]: http://inform7.com/