What is MoSoSo?   It’s a cool, hip abbreviation for Mobile Social Software.  It’s not new, but it’s buzzworthy again because Dustin Moskovitzand (Facebook c0-founder) and Justin Rosenstein (Facebook and Google) announced they were leaving Facebook to go work on a project that’s expected to be some kind of social networking appplication for business.  According to Justin’s blog:

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.

What can we expect from a business-focused social networking application? It’ll be available from both your smartphone and your desktop. It’ll have GPS and Google Maps and presence technology that offers the user choices and control. It’ll address the privacy and security concerns that have prevented many businesses from taking Facebook seriously. 

So why couldn’t Dustin and Justin stay at Facebook and build their productivity software inside? My guess is that it’s because their new product will be subscription-based —  and unlike Facebook or any other social networking app so far — it will make money.