Here you can find downloads for Wicked Engine, the free and open source 3D engine.

You can download the latest version of the development build with most up to date features below (look for Nightly build artifacts to download packaged executables):

The store versions can be outdated compared to the development builds, but they support automatic updates:

The source code is hosted on Github (using this allows C++ devlopment)
The C++ documentation can be read on Github
The LUA scripting documentation can be read on Github