Wolf is a cross-platform modern game engine.
Successor to the GAIL engine.
Consisting of 40+ libraries (and counting!), the engine provides support for a variety of functionality on an as-needed basis. Everything from low level systems (rendering, virtual file system, threading, time, run loops, etc) to high level (GUI, resources, etc.) are all available and can be used with each other.
The Wolf engine is designed primarily for desktop computers, specifically Linux, Mac OSX and Windows. However, it also has support for mobile systems (specifically Android, iOS), basic support for HTML (via Emscripten), and some support for even more esoteric platforms (BSDs, Haiku, even GNU HURD). It supports multiple architectures (x86 and ARM primarly, with some PPC support) and multiple compilers (GCC, Clang, MSVC). Wolf does all this via a system of 'drivers', which provide support for each platform, while retaining a common interface for applications to use. A game or program is written once on top of Wolf, and Wolf handles all the rest.
Wolf is written using C++11 and takes advantage of many modern compiler features. Its rendering system also uses modern GPU buffer allocations, and has experimental drivers supporting the next generation of rendering (Vulkan/DirectX12/Metal).
In fact, this website is written using these: