Gears of War 3 was in development for PlayStation 3
Epic Games was apparently working on bringing the third entry in the Gears of War series to PlayStation 3.
Gears of War was one of the biggest new franchises of the last generation, and it's often considered one of the reasons that Xbox 360 dominated the console market in the west. But Gears of War was never a Microsoft series, it was developed and owned by Epic Games, and there were occasional rumours back in the day that the series would be released for Sony's console.
And it turns out it actually was at least fairly closed that it happened. The Twitter user PixelButts has examined the huge Epic Games leak from 2011 and made a really nice discovery, as it turns out Epic was in fact working on a Gears of War 3 version to Playstation 3 - and there is even video proof of it. We don't know why it was never released, but we assume some kind of deal between Epic and Microsoft was made.
After Gears of War 3 was released back in 2011, Epic released a final game in the series called Gears of War: Judgment early in 2013, and just one year later, Microsoft bought all rights to the series from Epic.
Update: The following statement was sent to Kotaku:
"This footage is a byproduct of Epic's internal Unreal Engine 3 testing process, which utilized both Gears and Unreal Tournament, and was never part of any actual product work for PlayStation 3."