This will make for an excellent HN post once people can actually try it. Landing pages with email signups aren't a great fit for this site, though this is an impressive one.

That's a beautiful landing page. Kudos.

Something tells me this isn't going to be free. Although the landing page might leave you with the idea that is.

The website (features section) says that the library will be open-source.

It says the API will be open source, so maybe the tool itself won't. We'll see...

Seems strongly inspired by Macromedia Flash/Studio, the authoring application for creating Flash animations.

Hilarious, my first reaction at seeing the landing page was, "oh that interface.. haven't seen that in a while.. haven't touched flash in a looong time..."

Not a bad thing, considering animation with Flash was such a delight.

I wish something like this existed as a desktop app to output animation spritesheets from drawings.

The only application that works on Mac OS that does that is Flash. You can draw something, make it "tween" to a new position/rotation/size etc and output .pngs.

There is Spine and Spriter. They both support what you want (and much more).

The ghosts are cute.

Looks pretty sweet. I can't see much use case for it though to be honest. Animation's while reading is distracting, but maybe it could be useful for some interactive tutorial.

So you can export as GIFs? That would be cool, but I am skeptic.

LE: I say this because the animations on the site are gifs, and I assumed that they were made with spiritjs itself.

This is so excellent and looks fun. I'm really unconfident with my web animating abilities, and I feel I can learn a lot from this project! Thanks!

Strange that all of the animations under "Features" are gifs, and not actually animated by spirit.js.

Yeah, that's what I said. Maybe the tool has an export as GIF feature, which would make it awesome :)