While there's already Unigine Valley that was a recently-released tech demo / benchmark for OS X, Linux, and Windows, there's now Unigine Helicopter on the horizon. Valley was their most visually impressive tech demo yet and can throw any PC to its knees, helicopter is looking to continue this trend.
The actual demo isn't being released today, but only a demo. It was just this weekend when first talking about the latest Unigine Engine work. Besides new art assets, this helicopter demo is powered by their latest revision of the Unigine Engine and all of the goodies it offers.
Embedded below is the current trailer of Unigine's in-development helicopter demo. While details haven't yet been announced concerning the demo's actual release, you can expect that when released there will be a Linux binary.