"I was reading on Gamasutra about 'Is free-to-play ethical?' and all that kind of thing, talking about monetization and Skinner Boxes," Adams tells me. "We're very fortunate that we've escaped from having those concerns, and managed to make a living somehow."
Indeed, the way in which Dwarf Fortress is funded -- a completely free game that survives via donations from players -- is a far cry from the various business models that are carted around in the modern video game industry.
Adams reckons he knows exactly why his business model works for him, but wouldn't work for many others.
"We're not searching for a million-dollar hit, which is the feeling I get from other people -- what they are searching for when they release on iPhone and so on," he notes. "That's not everybody, of course. But we don't have to work that hard anymore, thinking about exactly how we're going to monetize."
"I've seen what people go through," he continues. "Rocketcat Games (Punch Quest) lives out here, and we meet up with him sometimes. And it's just a struggle, right? To decide how you wanna set up your free-to-play model. His was, what, too generous? So it didn't work out. Those kind of decisions, we've been very fortunate to have enough wiggle-room to bobble the ball completely, which is what we're doing."
Those who have followed the Dwarf Fortress story will know that Adams sends out crayon drawings to people who donate money, and adds them to a "Champions' List" -- a rather different proposition to what game developers offer nowadays.
"I mean, that's just completely weird, right?" he laughs. "But fortunately we don't have high demands, we don't need a lot of money, and we're making just enough to tread water. $50,000 for two people a year."
"I guess it's like shareware," he says of his own monetization technique. "We didn't really take inspiration from anything. Someone said to us, 'Why don't you put up a PayPal button for your birthday so I can send you $50?' And then over the next four or five months, we made around $300. I was still working then, and Dwarf Fortress wasn't even out. Then we released the game, and started making $800, $1000 in the subsequent months. And we were like, 'Maybe we actually have a shot.' Now we're averaging $4000 a month, baseline, which is crazy."
With Dwarf Fortress making $50,000 a year from donations alone, I questioned what sort of spread of donations Adams received. I'd assumed (correctly, as it turned out) that it isn't simply a bunch of people paying small amounts, but rather, Dwarf Fortress has its own "whales" -- people paying silly, unnecessary amounts.
"There's a subscriber system now, just because people asked for it," he tells me. "There's people who have given four-figure amounts. But these are not people who we necessarily haven't talked to before -- all of them send in their regards ahead of time, and they all know exactly what they're getting, because they've all been playing the game for ages -- years, in some cases -- before they send anything. They're not getting any sort of compensation for it besides some sort of story."
"I guess there are lots of parallels to be drawn between the whale system," he continues, "but there are people who give recurring money and large amounts. Some people have donated computers. Some people have donated their time -- there's a lot of volunteers handling the bug tracker and answering questions for people. There's the guy who did the port for Mac and Linux -- that was all free."
Everyone just wants to see Dwarf Fortress development continue, he reasons, so if they like the game, it's in their best interest to throw some money his way.
"I guess you could say the whale has an interest in receiving their present," he adds. "It's obviously a spectrum of giving -- a spectrum of ethical behavior. I don't know enough about what goes on in other markets to pass judgment offhand, but I know people talk about that."
While the Adams brothers are very clearly indie developers, it's notable that the pair rarely converses with other indie devs, or gets involved with the "indie scene" at all.
"It's not a deliberate thing," Adams tells me. "It's part of a personality thing, if anything. I didn't have many friends growing up, and didn't feel the need to hang out with anybody. So with Dwarf Fortress, I don't really see the upside. I've never really been a Twitter/Facebook kind of guy. I mean, it's fun to watch people talk to each other, but it's never the sort of conversation I would participate in."
That's not to say that the brothers don't ever participate. As previously mentioned, they've met up with Rocketcat Games and sampled a wide variety of mobile games that they wouldn't ordinarily have tried. Plus, the pair went to the EVE Fanfest earlier this year in Iceland, with Adams as a speaker -- "we accepted it because, you know, it was cool!"
But in general, Adams isn't so keen on socializing with other devs. "Things like GDC to us, were not a place we were invited to go," he says. "It was a place that you paid to go. And all the expos too. And networking never made sense to us, because of the nature of our situation."
"It's not like we're going to look for a job if this doesn't pan out -- we're not going to go and work for another studio or something," he continues. "We're just not interested in doing that. So there just hasn't been a need for it, even though I'm sure we'd benefit from it a lot. We don't feel like talking about the craft of game design or whatever. We kind of have a mature process, I guess, since we've been doing it for 13 years."
Although Adams has a PhD in mathematics from Stanford University, and taught mathematics for a short while, he says that his lack of drive to socialize stunted his mathematics PhD work somewhat. As he points out, mathematics is a very social field, at times.
"As much as you imagine people in closets working out theorems in the dark or whatever, it's all about co-authoring papers and not stepping on each other's toes, and working together on things because it's so complicated," he says. "I'm just not a socially-constituted person, I guess."
But despite his lack of social skills and his hiding himself away while he works on the game of his life, Adams is perfectly happy with where he is, and how the future is looking.
"I'm really satisfied with how things have turned out," he explains. "Having spent 13 years, you can kind of talk about 20 years without seeming like a total prat [laughs]. But we fully recognize that when you're talking about two decades in the future, who knows what the heck's going to be going on, right? Anything could happen. We'll be entering the age of health problems. Economic this and that."
"But I feel more at ease," he adds. It was something I never felt in mathematics when I was working on that stuff. I never reached a milestone like that. But who knows what's going to happen next."