It's also more than that, though. Any kind of choice-response interaction can be written in this: Courseware for schools. Quiz games. Lifepath systems for RPGs. In some ways, it's like the old PILOT programming language, but not bad.
Additionally, I prefer to work closed-source, so bug reports will be requests in English, rather than demands to install patches which may not match my vision for the system. If, years down the line, I end-of-life GameScroll, I will release it under a BSD-like license, as I do with all of my old software.
And, really, how does the source help you? Adventures made with it are more useful. If you think it's missing something, please let me know.