Another game engine Xenko from Silicon Studio, is available for free (at least for version 1.x according to their website). You can use it for open source and commercial projects, and its source code also available on GitHub. No royalties, no license fees. Not sure whether the higher versions (2.x and up) will be available for free as well.
Xenko real time demo (called Rescue Drone) was presented in CEDEC 2015, and it looks quite good.
At this time, Xenko is still in Beta phase, and the latest version is 1.5-beta. No Linux and Mac OSX version yet, although it’s already been successfully ported and tested internally by Silicon Studio. For Android and iOS development you’ll need Xamarin. Console support is on the way as well.
Xenko installer file is 15MB. This installer will download and install all run-time requirements necessary to use the GameStudio and develop on Windows. Xenko is using an auto-updating system, so your install will always be synchronized with the latest version of Xenko.
I have Xenko 1.4-beta installed but haven’t try it extensively, although at a glance Xenko GameStudio interface is similar to Unity and UE. Xenko documentation is still for version 1.0.0 though, but it covers most of the basic stuff in Xenko.
I’ve tried and updated Xenko to 1.5.3-beta. I can build the animation project sample, but can’t run it, and got an error message saying that I should push the optimization level up. Their forum is, meh, I think they are using the wrong kind of forum engine, it’s quite hard to find something or navigate their forum. (>_<)
The engine is slow about updates and documentation is lacking. I think they are working on the engine as an extra activity, and not as a full time job.
Does it have full C++ source? Getting deep into project and engine just to find out bug that you cannot fix is something i want to avoid.
Unreal is a bit too ahead of its times for mobile market, so some engine that actually can run simple game on most devices could be nice for next 4 years while >average< mobile hardware grows up to unreal demands. Currently is very hard to keep unreal game below 100mb and its very hard to sell game above 100mb.
From their website, Xenko is using the latest features from .NET 4.6 and C#6, so Xenko does not use C++?
Also Xenko 1.x.x source code can be downloaded from GitHub. Xenko website does not communicate clearly whether their source code will be available as open source forever or not.
So I watched that demo, and I can’t say I’m hugely impressed. The materials on the animated mechs are quite reasonable, but the demo as a whole is lacking. It basically consists of the two mechs and a chair, all of which are rendered using similar metallic materials. I’d be concerned that it isn’t too great for games like applications and cannot really render too many objects, nor is the renderer versatile to render many different types of object.
