Apprised is a social proof and conversion optimisation platform for websites that displays recent activities like sales,signups and purchases on your website to your visitors. It also helps in collecting emails and feedback from the visitors.

The Leverage FeatureBox widget helps build your email list with high converting opt-in feature boxes that turn your website visitors into subscribers.

Plugmatter Optin Feature Box is the Only List Building Plugin that Allows You to Create High Converting Optin Feature Boxes for Your WordPress Site.

Easily subscribe to a P2 comment thread without commenting using a "Follow" action link like WordPress.com has