Thanks! It's actually created with TigYog [1], a platform I'm building to let people write these kinds of interactive stories/lessons. It's somewhat influenced by things like Twine, but:
* It emphasizes "mostly-linear narrative" rather than "exploring rooms in an open world"
* It emphasizes using interactive fiction for education (e.g. features for "correct answer")
* It emphasizes writing over programming (e.g., no explicit variables)
* It has a WYSIWYG editor that feels kinda like blogging