It’s finally on Linux!
"Unity 4 Linux standalone desktop publishing preview
The most requested feature from our Community arrives in Unity 4. Port your standalone 32 or 64-bit desktop game with the new free Linux publishing preview. With the success of the Humble Indie Bundle and Ubuntu Software Center, and the popularity of Linux for crowd-funded games, you don’t want to wait to bring your game to a market eager and willing to pay for high-quality interactive content.
The Linux desktop publishing preview is a work-in-progress. The Linux OS runs on a variety of hardware and utilizes different software. It will take more testing and feedback before Unity ships a final version. Many games will run without Linux-specific problems on most modern Linux systems. While in preview mode, we will only be offering official support for Ubuntu 10.04 or later, with a graphics card that has vendor-made drivers installed. We encourage you to report any problems you encounter to us so we can fix them for the final version."