Here's the
Speare Website. It's pricey, in my book; partly because it's subscription based, so you have to keep paying ($4.95/month paid annually).
It's not really unique. It does automatically sync on multiple devices (Web, iOS, Android, etc.).
You could do pretty much everything it does with cards/sticky notes/paper.
Other apps to look at:
Bear.app (iOS and macOS)
Ulysses
Scrivener
Any number of
mindmapping and outlining apps.
The basic idea behind Speare is helping writings with prewriting, with the rhetorical stage known as invention (generating and organizing ideas).
Freewriting and brainstorming are techniques that Speare uses, but you could use any text editor or word processor or pencil and paper to accomplish the same thing, using the same techniques.