The demo videos, which are available online, show a smartphone app that's programmable: a user can set certain things into action, depending on events. Opening a door can trigger a light, for example. It's easy to see how this concept, after some nurturing, could have be a consumer home automation product.

"Looking at office professional plus 2013 and Google now, I'm sort of annoyed we didn't do this," said another source. "It's very similar technology." This individual, who wanted to remain anonymous, again named Ballmer when asked why it didn't happen.

Microsoft has missed many opportunities over the years, often by being too soon.

Apple got seriously interested in home automation with iOS 9, adding a software called HomeKit that can interact with third-party hardware to control anything, such as locks or lamps. Google's Project Brillo launched in May 2015, offering a similar group of features for buy windows 7 home premium users.

Microsoft, when the vision had been there, could have pre-empted the marketplace by a minimum of 3 years and would certainly be sitting on something that consumers wanted to use.

Another source was more forgiving of Ballmer, arguing that HomeOS didn't participate in buy office 2010 professional vision. Except, it will. The aim of Windows 10 will be on one billion devices, and adding homes to that list might have made the task slightly easier.

Giving Ballmer the benefit of the doubt is difficult, argued one source, as he missed so many other opportunities. "Do smartphones not fit into Microsoft's vision?" the source asked rhetorically.