Twitter is listless no longer. Following in the footsteps of Facebook, the increasingly popular platform has given its users the ability to sort other Twitter users into lists. “The idea is to allow people to curate lists of Twitter accounts,” Twitter’s list feature project lead, Nick Kallen (@nk), explained.

For example, you could create a list of the funniest Twitter accounts of all time, athletes, local businesses, friends, or any compilation that makes sense.

Lists are public by default (but can be made private) and the lists you’ve created are linked from your profile. Other Twitter users can then subscribe to your lists. This means lists have the potential to be an important new discovery mechanism for great tweets and accounts.

We started working on this feature because of the frequent requests we received from people who were looking for a better way to organize information on Twitter.

The company began rolling out the feature last month, gradually expanding access among its users. By Friday, Twitter lists had been fully integrated. By Sunday, 6.5 million—yes, million—lists had been created. Twitter now features: humor lists and techie lists and breaking news lists and staff lists and World Series lists and health care lists and ‘wits’ lists and media lists and media thinkers lists—and lists of lists and feeds of lists and rankings of lists and guides to creating lists and guides to using lists and guides to choosing lists and guides to list etiquette.

And among those watching the lists roll out, we’ve seen the typical new-technology-rollout combination of existentialism (What Do Twitter Lists Mean?), proclamation-making (“Twitter ‘Lists’ Change Everything”), and hand-wringing (“Twitter Lists: I’m Not Down”)—some of it valid, some of it less so. Twitter lists are exclusive. (Of course they’re exclusive; that’s the whole point.) Twitter lists are a popularity contest. (Only if you let them be.) The lists are a pain to create. (Not really.) And, either way, they’ll likely increase online serendipity and engender a curatorial economy and create a more efficient page rank system and suggest new ways to measure influence and empower political activism and maybe even replace RSS readers as users’ content aggregator of choice.

The ultimate validity of many of these claims—be they of the listophilic or -phobic variety—remains, at this early stage, to be seen. One thing, however, seems clear: Twitter lists are likely moving us closer to the full realization of last year’s quote-heard-round-the-Web: “If the news is that important, it will find me.”

What that means in turn, though, is a shift not just as concerns the cold, hard facts of Twitter: ‘influence’ metrics and aggregative utility and ‘economies’ of various stripes, etc. In means a shift as well in the platform’s foundational function: Twitter is—in addition to, and in many ways above, everything else—a community. And it is a community, importantly, that has been essentially created by users: Twitter owes its current form to the innovations added, over the few years of its existence, by its users. Users created @ replies. They developed hashtags as a kind of real-time, proto-list, filtering feature. They devised Follow Fridays. They invented the retweet. They coined, in fact, the word ‘tweet’ itself—a shorthanded term for ‘Twitter post’ that Twitter, the company, initially resisted. (It failed.)

As Steven Berlin Johnson put it in his recent Time cover story on Twitter:

This is what I ultimately find most inspiring about the Twitter phenomenon. We are living through the worst economic crisis in generations, with apocalyptic headlines threatening the end of capitalism as we know it, and yet in the middle of this chaos, the engineers at Twitter headquarters are scrambling to keep the servers up, application developers are releasing their latest builds, and ordinary users are figuring out all the ingenious ways to put these tools to use. There’s a kind of resilience here that is worth savoring. The weather reports keep announcing that the sky is falling, but here we are — millions of us — sitting around trying to invent new ways to talk to one another.

What Johnson is describing, in clinical terms, is end-user innovation: decentralized development undertaken by a product’s consumers, rather than its suppliers. But what he’s describing more broadly is simply a collective—one with common languages, behaviors, ethical codes, rituals. A collective, in other words, that is also a culture.

Megan Garber is an assistant editor at the Nieman Journalism Lab at Harvard University. She was formerly a CJR staff writer.