Mightybell, a social network that officially launches today, is Bianchini’s latest attempt to bring social networking to smaller communities. Her previous startup, Ning, explored custom social networks and was focused on individuals. Now she’s taking a different tack with Mightybell, which aims to help small groups organize online.

Backed with $4.2 million in funding from First Round Capital and Floodgate, Mightybell starts with large groups called “communities,” which are organized around topic, purpose, course, or profession. Each community has a subset of groups called “circles,” where users can read and post content and talk to other users who are also interested in that particular topic.

While Facebook (FB) remains largely focused on connecting users with others they already know, Mightybell encourages users to discover folks they don’t based on factors such as common interests and location. To wit, when a user joins a circle, they’re prompted to virtually introduce themselves by typing out a mini-autobiography that appears to the existing members of that circle, almost like a status update.

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Mightybell has amassed 450-plus monthly active communities since it began beta testing one-and-a-half years ago, with beta testers such as American Express (AXP), The Bill & Melinda Gates Foundation and LeanIn.org, the initiative spearheaded by Facebook COO Sheryl Sandberg aimed at helping women talk openly about challenges to achieve their goals. (According to Bianchini, there are now nearly 13,000 LeanIn-focused circles in all 50 U.S. states and 50 countries.) Mightybell aims to monetize its communities using a software-as-a-service (SaaS) model. It’s free for up to 100 members for any organization and then after that, $2 for every member. For instance, both American Express and the Gates Foundation are paying customers.

A custom mobile experience for iOS and Android is “coming soon,” according to Bianchini, as are new recommendation features that will suggest people, events users might like, and relevant content, making Mightybell what Bianchini likes to call a “smarter” social network. Social media users are tired of carving out individual features as their own services, she adds.

“The real innovation I believe is going to come from these smarter social networks, and that’s where we want to be a leader,” Bianchini says.