It’s not every day that Mark Zuckerberg wants to buy your company.

Yet that was the situation faced earlier this year by two young technologists, Joe Hewitt and Blake Ross, who were working on Parakey, a secretive project intended to bridge the gap between a user’s desktop operating system and the internet.

Early in 2007, Zuckerberg, the founder and chief executive of the popular social-networking site Facebook, emailed Ross to invite him to a series of informal get-togethers with other rising Silicon Valley stars that would eventually include YouTube’s Steve Chen and Chad Hurley.

Out of those discussions came the notion that Ross and Hewitt should sell Parakey and come to work at Facebook.

But for Hewitt, 29, and Ross, 22, who earned their Valley cred by helping develop the first version of Firefox, the open-source Web browser that has taken large chunks of market share from Microsoft’s Internet Explorer, the decision was far from an easy one.

“It’s very hard to come to the conclusion that it’s no longer the right call to go at it on your own,” said Ross, a Florida native who got his start in the technology industry at the age of 14 interning at Netscape, in a recent interview.

Every day for a month, Ross and Hewitt debated the pros and cons of the deal, but what eventually sold them on the deal was a development within Facebook.

In May, along with opening the site to all users, Facebook introduced a development platform that would allow any programmer to create applications for use within Facebook.

“Ultimately it was the platform launch that tipped us. It was pretty extraordinary,” Ross said. Within a week of the announcement the pair had decided to sell.

“Mark knows what he’s doing,” said Hewitt of Zuckerberg in a separate interview. “I wasn’t quite clear initially on what he was interested in us for, but as I learned more about his vision for Facebook, it’s clear that he does have one and he’s aggressively executing it.”

While the Facebook deal caused a stir among venture capitalists and on tech gossip blogs, it was mostly regarded as a talent acquisition—Hewitt himself says he has turned down job offers from most of the technology giants, including Google and Microsoft.

But the Parakey deal does provide clues to Facebook’s ambitions.

You can bet that at any given time when they’re on their computers, people are either checking email, instant messaging, watching a video, working on a document or a spreadsheet, reading the news, or looking at or sharing photographs.

For the most part, doing all of these requires firing up a number of different websites and programs.

But what if there was one site that could handle all of these tasks? It could mean a more productive experience for the user. And for that lucky site, it would mean a very sticky, if not captive, group of users that would be attractive to advertisers.

That hasn’t happened, of course, because no one is the leader in all of these categories. Microsoft’s Word and Excel are ubiquitous on home and office computers. Yahoo has one of the most popular news destinations, and its site Flickr leads the photo-sharing category. Google’s YouTube is No. 1 for online video.

What’s more, the desktop and Web universes are still almost wholly separate. Moving data from one space to the other can be frustrating. Microsoft’s announcement this week of a Web version of its Office suite had critics griping that the company didn’t go far enough in extending online capabilities.

And that’s where Parakey comes in.

“Parakey was a way to unify websites and desktops so that there was no longer the idea of a desktop application. There were simply websites that you went to that were able to interface with your PC,” said Hewitt.

Inspired by the minimalist design sensibilities and intuitive user interfaces of Google’s search engine and various Apple products, and believing firmly that supposedly simple tasks like sharing photographs and videos were much harder to do in reality, the pair set out to create an environment even their mothers could enjoy.

Parakey works through the use of literal keys. Users can modify and view files through a browserlike interface, dragging special keys onto the groups of files they want to share with others.

Through the use of a small downloadable program, Parakey also lets websites interact with files on a user’s hard drive.

While melding the online and offline worlds is not a new idea—Google and Adobe have already released early versions of similar programs—what makes Facebook different, and also sheds light on the logic behind the potential implementation of a Parakey-like system, is the social-networking site’s development platform.

Instant-messaging and photo-sharing applications have already made their way onto Facebook, and while most of the applications are time wasters, it’s not hard to imagine a day when Facebook versions of more sophisticated applications will appear. That is probably Facebook’s bet anyway: If you offer a unified experience with applications of high quality, what’s the reason to go to another site?

What Parakey’s capabilities add to the equation is that now these programs would be able to interact with the treasure trove of documents, pictures, songs, and movie clips that are on each user’s own computer. And the process would be made much simpler than it is now.

Hewitt and Ross first met in 2000 while both worked at Netscape, but the idea for Parakey grew out of conversations between them a few years later.

At the time the technology media were heaping praise on Ross, who had become the face of Firefox, and venture capitalists were hot on their heels when word broke that Hewitt and Ross were thinking of starting a new company.

In total, the two college dropouts raised between $1.5 million and $2 million in two rounds of venture funding and began working on Parakey in 2005, telecommuting from their apartments in Palo Alto. When the Facebook deal was finalized this July, Parakey had only two employees: Hewitt and Ross.

Contrary to rumors that Facebook outflanked Google for Parakey, Hewitt said there were no other companies in the bidding. The pair received cash and Facebook stock in the deal, and according to the TechCrunch blog, Facebook paid less than $4 million for Parakey.

While Parakey may have been a small deal, it stands to become a big part of Facebook.

Asked if Facebook will integrate Parakey into its site, Ross said “definitely,” although he would not provide a timeline.

“I’m spending 100 percent of my time on Parakey and 100 percent on other Facebook projects,” Ross said. Considering that both Hewitt and Ross say they typically work 14-to-16-hour days, seven days a week, that might not be a stretch.

Hewitt, who now sits directly across from Ross at Facebook’s Palo Alto headquarters, hit the ground running in his first days on the job.

A New Jersey native, Hewitt built a version of Facebook that would be navigable by the browser of the new iPhone. At Apple’s next product launch in September, Steve Jobs showed off the new WiFi-enabled iPod by logging on to Facebook.

“There is Steve Jobs demoing Apple’s flagship product, an amazing new iPod, and he chooses to show the NY Times, Bob Dylan, and my baby, the Facebook iPhone site!” Hewitt wrote on his blog. “Is there a higher compliment you can receive in this industry?”

But devoting nearly every waking moment to Facebook and software engineering does have its drawbacks. When asked about his love life, all Hewitt can say is, “Facebook is my girlfriend.”