Hustle – Email & Newsletter Marketing Plugins for WordPress
Hustle provides a means to not only connect with popular services such as MailChimp, Campaign Monitor, Constant Contact, GetResponse, and Mad Mimi, but it also lets you target users through slide-ins, popups, widgets, and shortcodes.
So it’s more of a complete marketing suite that you can use to encourage subscriptions, along with other functionality. It also provides nifty features like social sharing and statistical data regarding opt-ins.
credit : WPMU DEV