Nationbuilder is a fully featured Customer Relationship Manager, for tracking engagement with your users across social media, email, your website, and even real life. It is also a Content Management System, (like Wordpress) but unlike Wordpress, it is proprietary software and costs a lot of money to use. Nationbuilder has a few flash themes that look fantastic, but in my opinion is a poor cousin of Wordpress when it comes to content management and usability.
However it can be a great tool for larger activist groups, and I love to help integrate the CRM with Wordpress or edit the Liquid templates and scss files to take it beyond the default offering and make it work for your organisation.
Check out how we've helped these environment organisations to use Nationbuilder, or get in touch to talk about how it might work for you.