EXCLUSIVE: Artists Public Domain just scored one of the most profitable sales in the history of Sundance. It’s celebrating a 10-year anniversary. But even if you’re in the film industry, chances are you’ve never heard of this nonprofit producer.

That’s just fine with them. The Gotham-based org spent much of the last decade happily operating under the radar, producing and financing noncommercial projects. But all that changed in January, when Fox Searchlight paid nearly $3 million for worldwide rights to its $150,000 sci-fi love story “Another Earth” out of the Sundance fest. Two months later, Sundance Selects nabbed U.S. rights to its co-production “The Forgiveness of Blood,” which landed the Silver Bear screenplay prize in Berlin this year.

The success of the company’s fourth and fifth features, however, comes with irony: even though the “Earth” budget more than doubled with delivery costs, it still earned nearly 10 times that amount before hitting theaters Friday.

But under APD’s 501(c)(3) charity rules, none of the filmmakers can profit from it.

“Our goal was always to make enough money from each production so we could make another one. We never thought about the day where we’d actually have more money than we knew what to do with,” says Hunter Gray, who co-founded APD with Tyler Brodie, his partner at for-profit producer Verisimilitude (“Half Nelson”).

“It’s the first time we’ve ever had a film that’s in profit,” he explains. “We’ve never held a fundraiser, we don’t have any employees and we have very little overhead. … No one on the board gets paid, and we can never take money out.”

Filmmakers and some producers can be paid deferred fees in the rare event an APD film makes money, as they will on “Earth,” but no one gets traditional profit points.

Gray understandably seems a bit surprised that a charitable film org, run solely on donations from Brodie and himself, went from being a side project supporting noncommercial fare to a top indie producer of hot microbudgeted films overnight.

“Our organization doesn’t have the manpower to churn out a bunch of these small films,” he says, or to oversee an open submission process awarding grants. “We’re hiring our first employee this year, and we’re now looking at other ways to benefit filmmakers and the indie film industry as a whole.”

Brodie and Gray launched APD in 2001 while running their former (for-profit) production outfit, Plantain Films (“The Ballad of Ramblin’ Jack”). “We funded a few documentaries at the time, and were trying to figure out a way to keep making them and have it make economic sense,” Gray says. “It was Tyler’s idea to start a nonprofit and do other things to help filmmakers as well.”

The pair assembled a board that included themselves, Plantain/Verisimilitude producer Alex Orlovsky (“Blue Valentine”), Journeyman Pictures founder Paul Mezey (“Sugar”) and then-IFP exec director Michelle Byrd (since replaced by her IFP successor, Joana Vicente, who also co-owns Open City Films). Starting small, they set themselves up as a supporting org to IFP, giving annual grants for the IFP Market awards lunch, the Gotham Awards’ “Best Film Not Playing at a Theater Near You” prize and general funding.

APD donated two editing rooms and small office space to select projects, all funded by Brodie and Gray. “The idea is not to just give a grant,” explains Vicente. “It’s ‘We’re going to help you make your film, and if the film doesn’t sell, we’re going to help get it out there,’ whether it’s renting theaters or some other form of distribution.”

Projects arrive via film industry contacts, random submissions and word of mouth, but the board members’ busy outside work schedules initially kept feature production on the back burner. “You don’t always have the time to support films of that size as a working producer,” says Orlovsky. “It’s that same ‘one for them, one for me’ thing that actors do.”

The bigscreen efforts began in 2008 with Azazel Jacobs’ “Momma’s Man,” a black comedy about a man who moves back in with his parents (played by Jacobs’ own mother and father). Like all APD projects, it was brought in and shepherded by a board member (Orlovsky), and the under-$200,000 Kino release made $100,000 in theaters. The experimental mockumentary “Memorial Day” had a limited 2009 release, and niche distrib the Film Desk took the India-based pickpocket drama “Zero Bridge” to a $10,000 theatrical gross this year.

What the board members didn’t expect — and no one in the industry could predict — was the explosion of interest in small films without stars among specialty divisions like Searchlight and Focus. It complicates a very practical question for APD: when is a project commercial or noncommercial?

“Just by definition, we can only do projects that wouldn’t otherwise get funded by a for-profit,” Gray says. “The definition is not hard and fast or budgetary — there’s no criteria you can pin it to. ‘Another Earth’ was presented to us as three sentences with some footage, and we signed on. The director (Mike Cahill) and lead actress (Brit Marling) started shooting on their own, and wrote it together. It was much easier to look at it then and say this was definitely a nonprofit project.”

There are no immediate plans for another feature — right now, the board members are busy recovering from “Earth,” Verisimilitude’s “Terri” and other projects. A 10th anniversary party is planned for this fall, and plans are in the works to use their Searchlight windfall for the greater good of the industry.

“In the future, Artists Public Domain is going to focus on ways to create more transparency in the distribution of indie films,” Gray says. “I’d like to see the reason for having APD go away, and have interesting films at least get their money back, get out there and get seen.”