Scripts to Capture Email Addresses Without Signups

A few years ago, I trialled a script that would capture email addresses from website visitors without them signing up. It mostly worked for US visitors. Not UK/EU due to GDPR. I can't for the life of me remember what the script was called.
Anyone know of scripts thaty do this?
Thanks

I doubt that something like this exists. Technically it's impossible.

Like @Algo says, it's impossible to directly do that, so to accomplish it you need to get creative, chaining metadata to essentially de-anonymize the visitor.

You see this type of thing in the news occasionally, like an analytics/tracking company implementing a "bug" (ie. "by accident" lol), or by a password manager grabbing some PII, or when anti-fraud companies attempt to build an open-source trust score, etc.

And so... if they're doing it "by accident" *cough cough* ... There are certainly people doing it on purpose (and making money off of it ). With that said, you're often walking into a legal grey-area when doing stuff like that.

There are a number of companies that offer this, such as https://www.rb2b.com/ but you need a lot of traffic for it to be worthwhile, they typically can only indentify usa visitors and only about 30% of them.

I think that would have had to be using some sort of security hole.
I know of no exploit that can get emails right now.
Maybe something that takes advantage of social media in some way?