A nice game, but I have a suggestion. Add weight to the balls that counteracts the mouses position, taking into account how far they are from the pivot in the middle. So as a ball rolls out to the edge you'd need to tilt the plane more and more to counteract it's effect and keep it flat.

Nice idea! The tilting of the board seems a bit jerky though and it's hard to get the mouse right on it - any chance it could be smoothened up?

I will see what I can do about the jerkiness. You don't have to put the mouse on the board, it works anywhere on the world, just measuring the offset from the initial press to the current position.

I have an idea to make it a bit trickier - instead of all the balls starting at 0 velocity, you could assign them a small value to start with just so you're forced to do something rather than sit there with them all accumulating in the middle!