When Mark Zuckerberg left Boston 10 years ago for Silicon Valley, no one knew how much his company would be missed. Now Facebook has come full circle, opening an engineering office in Kendall Square that’s working on problems that could be crucial to the company’s future. As Facebook Boston leader Ryan Mack puts it, his team is “thinking about the next few billion users”---and that will require major tech advances in databases, networking, and compilers. With Twitter, Amazon, and other giants expanding locally, the Boston area is fast becoming a critical front in the battle for talent and tech supremacy.

In other innovation news:

— Radius Health is back on the IPO train. The Cambridge biotech, which is working on a drug for osteoporosis, has filed to go public again after pulling its initial stock offering twice before.

— Our deal of the week involves two New Hampshire companies: Web tech firm Dyn is acquiring Renesys, which monitors Web traffic. Dyn now has more than 350 people and, together with Akamai, pretty much runs the Internet from the Northeast.

— And lastly, when will you be able to upgrade your robot the way you do your laptop or smartphone? Rod Brooks, the founder of Rethink Robotics, says software is now the key to what robots can do in the real world---but first you have to understand what people want them to do. In my case, that’s easy: hold onto my laptop and phone so I can get some actual work done.