What's the Name of the Pop ups when you enter a site?

I have been seeing those new javascript overlays or whatever they're called that when you enter a page, you're asked to provide your e-mail (or close the page). Anyone knows what they are called?

Also, can anyone recommend a good one (or how to make it)?

Thanks

The marketing term i'm not sure of,the code itself is called Lightbox and there are many alternatives to it just depends what you're doing