What are some alternatives?
When comparing Storybird and Storyboard That, you can also consider the following products
My Storybook - Make children's storybooks online for free.
Pixton - Our goal at Pixton Comics is to enable everyone in the world to make comics.
Fanfiction.net - The most popular fan fiction website in the world according to Wikipedia
ToonDoo - ToonDoo is a fun and easy way to create comic strips without having to draw.
Cowbird - Cowbird is a simple tool for telling stories, and a public library of human experience.
Clip Studio Paint - Powerful drawing and illustration tool.