Facebook Co-founder Dustin Moskovitz, Lead Engineer Justin Rosenstein Leaving to Start New Enterprise Software Company

Facebook co-founder Dustin Moskovitz, and lead engineer Justin Rosenstein, announced today that they will be leaving Facebook to start their own company together in about a month. Facebook has confirmed that the two will be leaving the company.

Rosenstein confirms that the duo will be leaving Facebook to “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.”

Famous for his enthusiastic email when he joined Facebook earlier last year, Rosenstein this afternoon wrote an extensive post about his decision to leave the company, which he has given us permission to share publicly. Justin writes:

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-softwar

e 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.