WIRED:LAST SUNDAY, I walked into the business heart of San Francisco, tapped on the closed offices of a profitable IT business, scooted into what looked like their main conference room, sat down, and started fixing bugs. I felt a little like an accountant breaking into someone's ledgers at night, and double-checking their book-keeping.

I was there for the “Twisted Sprint”, which is perhaps both slightly less fun and/or painful than it sounds.

But it was certainly enjoyable enough for me to sit there, working for no pay on my weekend at something – programming, bug fixing, documenting – that others get paid a lot more than I do to do full time.

I wasn’t visiting the sprint, which is coders’ talk for a sustained burst of collective programming action, with journalistic intent. I really was going because coding with others is my idea of fun.

But as one does when one is having fun, I worried about where this was all going. Surely, in the application of the law all good Catholics know something as enjoyable as this must be ever so slightly doomed?

Twisted is an open source project. Open source projects traditionally rely, at least partly, on the contributions of volunteers. Twisted has been around for almost a decade, and certainly hasn’t hit doom yet. Like other open source works such as Firefox and Linux, it has continued to grow and gain wider recognition over time, becoming the parent of dozens of other free code projects which rely on it.

In the case of Twisted, it also drives some of the tools underlying commercial and government institutions like Lucasfilm, Nasa, TweetDeck, and Canonical.

I would explain what Twisted does at this point, but that really is not germane to this column. (If you must know, it’s an asynchronous event-driven library for Python, which lets you write code with deferred promises instead of blocking functions; pray do not ask me to explain it again.) But what it really is, to me, is the very model of a well-managed, but itinerant, open source project.

It’s used by thousands of people, but has no true home except on the internet. What appears to drive its development is the enjoyment its engineers get from building it, and the deliberate openness of the project to new blood like me.

But men and women do not run on fun alone. Someone has to pay for the sandwiches I ate while sprinting. Someone paid for the laptop that Glyph, Twisted founder and honorary guy sitting next to me at the sprint, was struggling to install a new operating system on to. We all have day jobs – Ying Li, who organized this sprint, wasn’t doing it as part of her work as a technologist. Rackspace, the company generously hosting the sprint, weren’t expecting obvious and direct returns from the bug-fixing under their roof.

I’ve been talking about open source for as long as it has been called that, and about free software before then. It’s been heartening to see it grow and become as well-known in a wider circle than the far smaller core of geeks who championed it in the 1990s.

But the precision with which we described its merits back then was only matched by the fuzziness with which we explained its economic underpinnings or the nature of its incentives.

Is it enough that we are all doing this free work out of a sense of community spirit? And if we were all working for less money, in jobs that left us exhausted or dispirited, would we continue?

Or, as any number of cynics have told me over the years, are we just suckers?

A prominent Linux hacker of my acquaintance said they had stopped working on the project after meeting, at conferences, endless smug and unlikeable bankers who, they realised, were pursuing execrable goals from their efforts.

Vastly profitable edifices like Facebook and Google are built on the groundwork of open source software.

The companies are good citizens, to a point. They pay back in their own contributions of code, and they offer roofs to the best sprints and jobs to the smartest coders. But it’s noticeable they still have a few billion dollars of surplus value left over after all the sandwiches are eaten.

And coders aren’t the only ones. “Digital sharecropping” was how Nicholas Carr described the user-generated content boom of social sites like Flickr and Facebook.

It’s not hard to draw a line between the millions of dollars a photo site like Instagram made its creators, and the millions of photographs we collectively contributed to make it a success. We wouldn’t have enjoyed those pictures without Instagram; but Instagram’s creators would not be millionaires without aggregating our contributions.

Sitting here, looking over the beauty of Twisted’s code, I still think it’s a good deal. Free software seems, as it always did, like a elegant hack of economics and incentives, in that those who wanted millions would get it, and the rest of us would get free software and ideas that we could all share. But I wonder what happens when that economic balance shifts.

What happens when code makes no more billionaires? Will the old guard still keep us around?

And what happens if we decide to make software that replaces them?