This partnership will see Microsoft and Unity collaborating to add support for "enhanced Kinect gestures and recognition, multiplayer matchmaking, SmartGlass and cloud stuff" in Unity Pro 4 for Xbox One. If an outfit is using Unity to create a game for Microsoft Studios, then Unity tools for Xbox 360 and Xbox One will be offered gratis. Publishing games on the Windows Store will also be free.
Unity is one of the more popular multi-platform engines out there right now. In March, Unity announced it had entered a similar partnership with Sony to offer tools tailored to Sony platforms, including the PS4, and last month Unity made its mobile development tools available free of charge to all indie developers.