berlin-wall-downApp.net is today announcing a free tier, an expansion of its invite service that allows yearly customers — as opposed to monthly customers — to invite users to the service at no cost. The social-network-slash-app-development-framework is no longer limited to people who have $50 — it’s limited to people who know someone with $36 and an App.net subscription.

App.net founder Dalton Caldwell describes the free tier, which has evolved from an invite system that allowed annual subscribers to “gift” an App.net membership for 30 days, as an experiment. Like the invite system, he says, “This is another attempt to increase distribution without compromising on what the core values are.” The service won’t be overrun by free users, and Caldwell says that the paid service will remain at the core of App.net, but the introduction of a free tier will allow more people to use the service.

Free users will be able to follow 40 people on App.net, receive 500 megabytes of free file storage (which the company introduced in January), and can upload files up to 10 megabytes in size. These users must be invited by users with annual subscriptions, and have the option to use the free tier indefinitely or to remove the restrictions for $36 per year or $5 per month.

“I look at the data that has come through the free invites that we’ve experimented with the last few months, and the more casual users probably won’t notice that limit, but the more active, power users will,” Caldwell says of the restrictions on free users. “They don’t cripple the core product, it’s only once you’re really into it that you notice that there’s a real reason to pay.”

He compares this model to that of Dropbox or Evernote, which offer free versions of their services with the hope that some users will decide to pay for more advanced features. Given the sky-high valuations, rumored IPOs, and rapid expansion of both of those companies, both Dropbox and Evernote are pretty good companies to emulate.

Still, a free tier — especially one based on invites — isn’t a guarantor of success by any stretch of the imagination. Dropbox and Evernote both make simple promises to users, whether it’s keeping all of your files or just your digital archive in sync across devices, and consistently deliver on that promise. App.net is still making its way towards the realization of its promise to build an application framework for developers.

The free tier and the freshly-launched file storage service are meant to bring App.net closer to that founding goal. Though the service has been criticized as being “Twitter for people with $50,” as referenced above, App.net was never meant to be a social network. It’s an identity service that will allow users to carry their content and relationships across applications, with little hassle on the developers’ part.

Or, put another way: App.net is about taking a user’s content, login information, and relationships out of so-called data silos and putting them under the users’ purview. “In this model, if new, shiny stuff comes out that you want to try out, you get to bring it with you and it’s hosted in your file bucket rather than in the application’s silo,” Caldwell says. Someone might be able to sign up for a photo-sharing service without wondering what happens if it goes under, for example.

Allowing users to sign up for free is simply the latest step App.net has taken to reaching that goal. Whether or not it will turn into a true identity service that a meaningful number of developers bake into their applications depends on how well the community reacts to this new free tier and App.net’s willingness to pull the plug if things go poorly.

App.net is in the unenviable position of proving that it isn’t a social network despite the fact that, as it exists right now, that’s basically what it is. There are some apps, like the Patter chat client, that break from the “App.net is a Twitter replacement” mold, but for the most part that’s how users view the service.

So, yes, today’s announcement shows that App.net is more than a social network for people with $50. And the company has laid the groundwork to become more than a social network, period, with the File API. Now it’s time to see just how long it takes for App.net developers and users to look past its beginnings and embrace App.net as a development framework, not a Twitter alternative.