Good news, everyone!
The Horde3D GameEngine is now working on Linux, too. At least, most of the main components are.
May I direct your interest to this page in the GameEngine's Wiki:Building the GameEngine on Linux (experimental)
Currently, there is a Code::Blocks workspace file that contains all required projects (just like the Visual Studio solution). I chose this approach, because converting existing Visual Studio projects into Code::Blocks projects is so much easier
than maintaining CMakeLists or stuff like that.
Go ahead and give it a try. In the "Current Status" section on the Wiki page, you'll see what's currently working, and what's not. This will continuously be updated, when new features are made available for Linux.
Looking forward to hearing of your experiences with the GameEngine on Linux platforms.