I came across this beautiful site,

http://www.porte-sainte-claire.com

initially I thought this was Flash, but it is not.

I would guess this is Jquery, does anyone what sort of plugin this is?

Cheers.

that is brillaint jquery

It's unlikely to be a single plugin, instead it would probably use a few animation plugins which are used to create the effects you see

Impressive.

 

I can't imagine this is the result of a single plugin.

It's JQuery in conjunction with a CSS3 selector module like sizzle.