I built Pippity in 2011 and it was one of the first products that brought advanced features to opt-in popups for lead generation. The idea was that by making opt-in popups your readers don’t hate, they'll convert better... and it worked!
It used advanced triggers (end-of-article trigger, exit-intent, etc) and analytics to know if your opt-ins are driving away visitors.
It included connections to all major email providers and a wide selection of designs to choose from.