Linux Foundation's New Open 3D Engine Requires Windows and Visual Studio
phoronix.com
phoronix.com
Also, you should know Amazon's Lumberyard was basically just a copy of CryEngine that they purchased and began to modify. They must have spent a lot of money to be able to get full rights to that and now be able to make it OSS.
My bet, though? Amazon is axing the entire Amazon Game Studios, or at least radically changing how they operate - and part of that is hoping they can dump development of the engine on the OSS community and get momentum behind it.
One need only look at the titles[0] Amazon Game Studios has been developing to find they haven't been doing too well, given they started and cancelled the following titles after several years of development put into each one:
* Breakaway * Crucible * Lord of the Rings MMO * Intensity * Nova
And plenty more..