The Unity game engine, now powering video game development from the iPhone to the Xbox, is yet another emerging platform set to open its own “App Store”.

User numbers have soared since David Helgason, Unity chief executive, announced at its developer conference in October that a $199 version of its software would be free.

“Meticulously, in four and half years, we’ve built up 13,000 users, and then in a month we’ve more than doubled that,” he told me this week. Read more