MailChimp is a freemium email marketing tool. Similar to Wufoo, they offer a free plan (good through 2,000 contacts). A bit of background: MailChimp grew their business significantly when they decided to go freemium. How? At the bottom of every email, it would say something like Powered by MailChimp. Every customer email sent helped to spread the word. It created a kind of viral loop.
However, what Brunson cleverly conceived with ClickFunnels is to create a SaaS that can integrate with the world's most popular platforms and virtually anyone can quietly launch a funnel in hours as opposed to weeks of hefty coding and programming. As a fervent user of ClickFunnels myself, I can tell you that the system is impressive beyond measure.