The C4 Engine was ported to Linux in 2012 and supports Windows XP and newer, OS X, and PlayStation 4 as among the targets. The C4 Engine was started by Eric Lengyel who also founded Terathon Software, the company continuing to develop this proprietary game engine.
In announcing C4 Engine 4.2 today, Eric Lengyel wrote, "Linux support has been removed from the C4 Engine, effective in version 4.2. This decision was made based on the disproportionate cost, both in terms of time and money, that we incur to support Linux relative to a very small return on our investment. This decision was also made to preserve my own sanity since my personal experiences with Linux have been extremely negative and have resulted in huge wastes of time that could have been better spent on more productive tasks. Terathon Software will no longer contribute to the popularity of an operating system that I personally view as inferior in design to both Windows and Mac OS X. Linux has proven to be Frankenstein OS assembled from a disparate array of barely functioning parts with horrible reliability and little potential for future improvement. Time that would have been spent on Linux support will now be used to strengthen our product on platforms with much greater viability."
Eric seems to have run into a lot of Linux issues... Previously on Twitter he complained of not being able to install Ubuntu 14.04 and commenting he said that GPU drivers weren't much of a problem for Linux but "literally everything else is a complete disaster, including sudo apt-get."
C4 Engine customers needing Linux support can use C4 Engine 4.1 or older, including porting the old code to the new engine release, but Eric mentions they're forbidden from sharing that code with other teams. He says too in the future that they may support SteamOS but that they will not let the engine run on Linux in general.