The rumours of the Unity game engine
being ported to Linux have been confirmed true as
Unity Technologies opens pre-orders for Unity 4
Unity Technologies announced today the next iteration in the Unity game engine, Unity 4. Among the various upgrades to the engine was the inclusion of the ability to publish games to Linux platforms. The engine makers and game developers have mentioned the feature before, but this is the first confirmation of it being in the next version.
Unity 4, which can be pre-ordered today, also adds full support for DirectX 11. This allows for tessellation and much more advanced shader capabilities. The engine is still closed source, albeit available for free, and only runs on Windows and OS X. Some of the more famous games that run on the tech include downloadable platformer Rochard, and upcoming PC RPG Wasteland 2.
You can pre-order the Pro version of Unity 4 from the Unity store.