You can download the Storyboarder app on Wonderunit site.
Here is Storyboarder’s GitHub repo link if you feel like contributing.
And yes, it is an opinionated software. For instance the absence of layers is frowned upon by some. On the other hand this is a tool designed for the author’s purpose: visualising and blocking scenes fast within a certain type of constraints. The unique layer constraint is exactly what makes this app a good tool for drawing fast. You don’t get to draw in layers when you are Storyboarding on paper either.