Stack Overflow is the go-to site for millions of programmers, giving them straightforward answers to complicated technical questions.

The company's already moving fast on its next phase of growth, says CEO Joel Spolsky, selling private versions of Stack Overflow to businesses customers, including Microsoft.

Spolsky sees Stack Overflow as playing a crucial role in the software boom, helping programmers navigate the ever-more-complex world of technology.

Millions of programmers rely on Stack Overflow, the question-and-answer site for the tech industry, to do their jobs. So much so, that it's become something of an industry in-joke.

—The Practical Dev (@ThePracticalDev) March 4, 2016

It doesn't matter which programming language you're using, what kind of software you're trying to make, or where in the world you're located. If you have a question, one of Stack Overflow's 50 million monthly visitors likely has an answer. That's made Stack Overflow the premiere place for programmers to socialize and discuss important issues.

Joel Spolsky, the CEO of Stack Overflow, tells Business Insider that he sees the site as "the Library of Alexandria" — an archive of the web's collective programming knowledge. But Stack Overflow offers a lot more than programming tips. The nine-year-old company now operates a network of 170 topic-specific Q&A sites, including ones focused on travel, math, and office etiquette.

Next up for Stack Overflow: Moving into the lucrative business software market. Specifically, the company is selling private, internal-only versions of its site straight to big companies, a service it calls Stack Overflow Enterprise. The service has 14 customers so far, including Microsoft.

Recently, the company began beta testing a similar service for small businesses called Stack Overflow Channels. That service gives smaller teams their own roped-off Q&A sites.

Spolsky says that Stack Overflow Enterprise has been one of the easiest sales pitches of his career. He tells the story of a recent sales call with a major technology company, where he came fully prepared to state his case. Instead, once the company's representative heard that what he was pitching was just a version of Stack Overflow for the company's internal use, the rep was on board instantly.

"Oh yeah, we should probably have that," the buyer told Spolsky.

Real answers, not cat GIFs

There are a few factors that make private versions of Stack Overflow that are hosted on customers' own servers, so desirable, says Spolsky.

Among the biggest: it limits the audience who can see questions and requests for help. Asking a question to the entire public audience of Stack Overflow can be intimidating, Spolsky says. With the private service, developers are just asking for help from their peers, not random internet strangers.

"Some developers are just afraid of asking on Stack Overflow," he says.

And limiting the audience can also mean that developers can seek and get more specific answers. A Microsoft employee can't really ask about internal tools and procedures on an open forum. Even if the developer found someone who could help, having the exchange out in public might violate confidentiality policies.

An artist's rendering of the Library of Alexandria, which is best known as a major center of learning that was lost to the world following a great fire. Wikimedia Commons

The private enterprise service can also allow companies to build their own in-house "libraries" of knowledge. New employees can see the sum, collected wisdom of everyone who's come before.

There are chat services (like Slack, which he calls a "beautiful product") and internal website tools (like Atlassian Confluence) that also promise permanent archives of knowledge and discussions. But Spolsky draws some distinctions between them and his service.

Chats can be full of "cat GIFs" and cross-talk that make it hard to find answers to particular questions. And most people forget to update internal websites.

By contrast, a question-and-answer site like Stack Overflow is both intuitive and easy to search, he says. And it's to the point — you ask a direct question on Stack Overflow, you get a direct answer.

"We don't tolerate chit-chat," Spolsky says.

The legacy of Stack Overflow

Spolsky sees developers' reliance on Stack Overflow as a good thing. In the past — as Spolsky himself experienced — trying to get started as a programmer took a lot of effort. Finding the right tool for even the simplest of jobs was a matter of scouring books and magazines, writing away for trials on floppy disk, and, once you found a tool to test, hoping against hope that it actually worked.

But in recent years, there's been an "explosion" of technologies from startups and established players that have improved the situation for developers. Programmers can more easily build into their apps the ability to take payments, thanks to Stripe, or to send texts and make phone calls, thanks to Twilio. They can also tap into AI tools from companies like Google, Microsoft, and Amazon.

To Spolsky's mind, it's only something like Stack Overflow that's allowed the current software boom to flourish. With all of these technologies around, the traditional ways of solving software problems just can't keep up. Stack Overflow presents an ever-evolving, living record of how to solve the most present and pressing problems.

If Stack Overflow is successful, "you don't need the books anymore," Spolsky says. "That's kind of a high bar, but it's great."