This afternoon word that Dustin Moskovitz, co-founder of Facebook, was leaving to start a new venture start to spread and within a short period of time, a number of blogs had access to a Facebook note posted by Moskovitz’s developer companion, Justin Rosenstein. Apparently Rosenstein and Moskovitz are leaving to create an enterprise level productivity software package.

Sounds thrilling doesn’t it? Well, the duo is a geeky bunch and they are now moving on to live out a new tale. Best of luck to Rosenstein and Moskovitz on their new venture. If it is anything nearly as successful as Facebook it is sure to be a hit. Techcrunch received a comment from Mark Zuckerberg on the depature: “Dustin has always had Facebook’s best interests at heart and will always be someone I turn to for advice.”

As I posted a few hours ago, “Over the next few months we can only assume that there will be more executives to come and go.” I didn’t know that we’d learn about another executive to leave so quickly! Posted below is the note posted by Justin Rosenstein.

I was a nerdy little boy. (Not much has changed.) Starting at age ten, I would spend hours a day holed up in my room, alone or with friends, programming til I collapsed. When I grew up, I wanted to be a software entrepreneur. I knew this with as much conviction, and about as much knowledge of what the role actually entailed, as other kids might have wanted to be an astronaut or President. In high school, I even started “Smiley Technologies, Inc.” and bamboozled some friends one summer into working on a Java-based productivity suite for group collaboration… but by September we learned the hard lesson that it takes more than three months to take on Microsoft Office.

By college, I felt pretty confident I was never gonna work for anyone other than myself. That is, until I heard about Google’s associate product management program. I have an enormous amount of respect and admiration for Google, and the opportunity to be on the inside, working as a mini-entrepreneur, was just too sweet to pass up. So I promised myself I’d stay at Google for just a few years, and then head out on my own.

That is, until a few years later when I got a friend-request from Dustin Moskovitz, who had co-founded Facebook with his college roommates around the time I’d joined Google. I told him I wasn’t interested in another job, but we met up for lunch anyway, and I’m glad we did. The more I learned about Facebook, the more inspired I was by its mission and team, and eventually decided this too was just too important an opportunity to say No to.

I’m really happy I took the job. I’m thrilled with the time I’ve had at the company, and with the incredible peers I’ve gotten to know and work with. But something else exciting happened in the year and a half since I joined Facebook. I started spending a lot of time after work talking to Dustin. Efficiency-through-software was dear to his heart as well, and we would stay up til 3am raving about how shortcut keys and high-level abstractions would Change The World. We shared a passion for technology, for entrepreneurship, and for using them to solve the same set of problems.

As our visions for how productivity software could work came into alignment, we thought about building it inside of Facebook. It was an attractive option in many ways, and neither of us was eager to exit a company that was in such an exciting phase of its development. But at some point it became clear that doing so wouldn’t be good for Facebook or for us. Facebook needs to continue its mission of making the world more open through social software, without distraction, and the new project requires a company built around it from the ground up, with the goals of efficiency and group collaboration embedded deeply into its DNA from day 1.

So we’ve decided to leave Facebook (in about a month) and start a new company, to build an extensible enterprise productivity suite, along with a high-level open-source software development toolkit, built for the Web from the ground up.

We see this new venture as very complimentary to Facebook. We hope our products will become to your work life what Facebook.com is to your social life. Our software will use Facebook Connect as the default option for identity and authentication. Our user interface will adopt many of Facebook’s conventions, creating a seamless and familiar experience for current Facebook users. And if our new development tools turn out to be useful, we hope the Facebook engineering team will come to adopt them.

Leaving Facebook makes me sad, but I feel I have to follow my passion on this. I can’t say enough about Facebook and the friends I’ve made here, and I am enormously excited for the company’s further success, a destiny I’m confident it will reach regardless of my participation in it. Finally, I’m really grateful to Mark, Chris Cox, Sheryl, Yishan, Chamath, Elliot, and others, who’ve been helping us make this a smooth transition, and to my family for guidance and support. Thank you; it’s meant a lot to me.